Can't find *.objs folder when buildsInSource option is enabled in esy

Nobody has claimed this yet.

I am not 100% sure it's because of `"buildsInSource": "_build"` option in esy, but in `reason-reactify`, where that option [is enabled](https://github.com/bryphe/reason-reactify/blob/master/package.json#L13), RLS doesn't seem to be able to find the object files.

It seems to be looking in `_esy/default/...` but the `.objs` folder is in `_build/default/...`:

```
Unix.Unix_error(Unix.ENOENT, "opendir", "/Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/../../lib/.reactify.objs")
```

The debug log doesn't seem to include any relevant info (it crashes as soon as an `.re` file is opened) but here it is fwiw:

debug.log

```
Hello from /Users/javi/.vscode/extensions/jaredly.reason-vscode-1.4.0/bin.native
Previous log location: /var/folders/ss/97gmv_jn031f29dsvb600f280000gn/T/lsp.log
Sending notification {"jsonrpc": "2.0", "method": "client/registerCapability", "params": {"registrations": [{"id": "watching", "method": "workspace/didChangeWatchedFiles", "registerOptions": {"watchers": [{"globPattern": "**/bsconfig.json", "globPattern": "**/.merlin"}]}}]}}
Sending response {"id": 0, "jsonrpc": "2.0", "result": {"capabilities": {"textDocumentSync": 1, "hoverProvider": true, "completionProvider": {"resolveProvider": true, "triggerCharacters": ["."]}, "signatureHelpProvider": {"triggerCharacters": ["("]}, "definitionProvider": true, "typeDefinitionProvider": true, "referencesProvider": true, "documentSymbolProvider": true, "codeActionProvider": true, "executeCommandProvider": {"commands": ["reason-language-server.add_to_interface_inner"]}, "codeLensProvider": {"resolveProvider": true}, "documentHighlightProvider": true, "documentRangeFormattingProvider": true, "documentFormattingProvider": true, "documentFormattingProvider": true, "renameProvider": true}}}
Read message
{"jsonrpc":"2.0","method":"initialized","params":{}}
Read message
{"jsonrpc":"2.0","method":"workspace/didChangeConfiguration","params":{"settings":{"reason_language_server":{"location":"","refmt":"","lispRefmt":"","format_width":"80","per_value_codelens":false,"dependencies_codelens":true,"opens_codelens":true,"show_module_path_on_hover":true,"reloadOnChange":false,"show_debug_errors":false,"autoRebuild":true}}}}
Read message
{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///Users/javi/Development/github/reason-reactify/examples/dom/WebReconciler.re","languageId":"reason","version":1,"text":"/**\n * This is an implementation of a reconciler for DOM elements via js_of_ocaml :\n * http://ocsigen.org/js_of_ocaml/3.1.0/api/Dom_html\n *\n * This is just an example but you could use this to create interesting\n * CLI apps, with a react-like functional API!\n*/\nmodule Reconciler = {\n /*\n Step 1: Define primitives\n */\n type imageProps = {src: string};\n type buttonProps = {src: string};\n type primitives =\n | Div\n | Span(string)\n | Image(imageProps);\n\n /*\n Step 2: Define node type\n */\n type node =\n | Div(Js.t(Dom_html.divElement))\n | Span(Js.t(Dom_html.element))\n | Image(Js.t(Dom_html.imageElement))\n | Container(Js.t(Dom_html.element));\n let document = Dom_html.window##.document;\n\n /*\n Step 3: Implement a create function\n */\n let createInstance: primitives => node =\n primitive =>\n switch (primitive) {\n | Div => Div(Dom_html.createDiv(document))\n | Span(s) =>\n let e = Dom_html.createSpan(document);\n e##.innerHTML := Js.string(s);\n Span(e);\n | Image(p) =>\n let img = Dom_html.createImg(document);\n img##.src := Js.string(p.src);\n Image(img);\n };\n\n /*\n Step 4: Implement remaining primitives\n */\n\n let _getInnerNode = node =>\n switch (node) {\n | Div(e) => e |> Dom_html.element\n | Span(e) => e |> Dom_html.element\n | Image(e) => e |> Dom_html.element\n | Container(e) => e |> Dom_html.element\n };\n\n let updateInstance =\n (node: node, _oldPrimitive: primitives, newPrimitive: primitives) =>\n switch (newPrimitive, node) {\n /* The only update operation we handle today is updating src for an image! */\n | (Image({src}), Image(e)) => e##.src := Js.string(src)\n | _ => ()\n };\n\n let appendChild = (parentNode: node, childNode: node) => {\n let innerNode = _getInnerNode(childNode);\n switch (parentNode) {\n | Div(e) => Dom.appendChild(e, innerNode)\n | Span(e) => Dom.appendChild(e, innerNode)\n | Image(e) => Dom.appendChild(e, innerNode)\n | Container(e) => Dom.appendChild(e, innerNode)\n };\n };\n\n let removeChild = (parentNode: node, childNode: node) => {\n let innerNode = _getInnerNode(childNode);\n switch (parentNode) {\n | Div(e) => Dom.removeChild(e, innerNode)\n | Span(e) => Dom.removeChild(e, innerNode)\n | Image(e) => Dom.removeChild(e, innerNode)\n | Container(e) => Dom.removeChild(e, innerNode)\n };\n };\n\n let replaceChild = (parentNode: node, oldChild: node, newChild: node) => {\n let newInnerNode = _getInnerNode(newChild);\n let oldInnerNode = _getInnerNode(oldChild);\n switch (parentNode) {\n | Div(e) => Dom.replaceChild(e, newInnerNode, oldInnerNode)\n | Span(e) => Dom.replaceChild(e, newInnerNode, oldInnerNode)\n | Image(e) => Dom.replaceChild(e, newInnerNode, oldInnerNode)\n | Container(e) => Dom.replaceChild(e, newInnerNode, oldInnerNode)\n };\n };\n};\n\n/* Step 5: Hook it up! */\nmodule JsooReact = Reactify.Make(Reconciler);\n\n/* Define our primitive components */\nlet div = (~children, ()) => JsooReact.primitiveComponent(Div, ~children);\n\nlet span = (~text, ~children, ()) =>\n JsooReact.primitiveComponent(Span(text), ~children);\n\nlet image = (~children, ~src, ()) =>\n JsooReact.primitiveComponent(Image(src), ~children);\n\n/* Create a container for our UI */\nlet container =\n JsooReact.createContainer(\n Reconciler.Container(Dom_html.getElementById_exn(\"app\")),\n );\n\n/* Let's finally put our UI to use! */\nlet render = () =>\n ;\n\n/* First render! */\nJsooReact.updateContainer(container, render());"}}}
Found a `dune` file at /Users/javi/Development/github/reason-reactify/examples/dom
]] Making a new jbuilder package at /Users/javi/Development/github/reason-reactify/examples/dom
=== Project root: /Users/javi/Development/github/reason-reactify
Detected `esy` dependency manager for local use
=== Build dir: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0
Get ocaml stdlib dirs
Include subdirs? no :/
Got a compiled base /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/.WebReconciler.eobjs
Local file: /Users/javi/Development/github/reason-reactify/examples/dom/WebReconciler.re
Local .cmt file: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/.WebReconciler.eobjs/WebReconciler.cmt
Other directory: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/../../lib/.reactify.objs
Sending notification {"jsonrpc": "2.0", "method": "window/showMessage", "params": {"type": 1, "message": "Unix.Unix_error(Unix.ENOENT, \"opendir\", \"/Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/../../lib/.reactify.objs\")Raised by primitive operation at file \"util/Files.re\", line 185, characters 7-24\nCalled from file \"src/analyze/FindFiles.re\", line 154, characters 17-47\nCalled from file \"src/analyze/State.re\", line 381, characters 24-253\nCalled from file \"_none_\", line 0, characters 254-1023\nCalled from file \"util/Infix.re\", line 7, characters 110-120\nCalled from file \"list.ml\", line 117, characters 24-34\nCalled from file \"src/analyze/State.re\", line 366, characters 39-1023\nCalled from file \"src/analyze/State.re\", line 538, characters 24-75\nCalled from file \"src/lsp/NotificationHandlers.re\", line 75, characters 24-72\nCalled from file \"src/lsp/BasicServer.re\", line 84, characters 11-35\n"}}
Read message
{"jsonrpc":"2.0","id":1,"method":"textDocument/codeAction","params":{"textDocument":{"uri":"file:///Users/javi/Development/github/reason-reactify/examples/dom/WebReconciler.re"},"range":{"start":{"line":117,"character":23},"end":{"line":117,"character":23}},"context":{"diagnostics":[]}}}
[server] Got a method textDocument/codeAction
[server] processing took 0.00596046447754ms
Found a `dune` file at /Users/javi/Development/github/reason-reactify/examples/dom
]] Making a new jbuilder package at /Users/javi/Development/github/reason-reactify/examples/dom
=== Project root: /Users/javi/Development/github/reason-reactify
Detected `esy` dependency manager for local use
=== Build dir: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0
Get ocaml stdlib dirs
Include subdirs? no :/
Got a compiled base /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/.WebReconciler.eobjs
Local file: /Users/javi/Development/github/reason-reactify/examples/dom/WebReconciler.re
Local .cmt file: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/.WebReconciler.eobjs/WebReconciler.cmt
Other directory: /Users/javi/Development/github/reason-reactify/_esy/default/store/b/reason_reactify-967a3fa0/default/examples/dom/../../lib/.reactify.objs
```

The failure path is shown in util/Files.re, src/analyze/FindFiles.re, and src/analyze/State.re; start by tracing how the esy build directory is selected for buildsInSource. Done means the existing .reactify.objs location is found without the ENOENT shown when opening examples/dom/WebReconciler.re.

Written by the indexing model from the issue text.