Shadowing definitions break type hovers

Consider a module:

```ocaml
module Foo = struct
let a b = b + b
let c d = a d
let a b = b + b
let d f = a f
end
```

A hover on the first `a` will work, but hovering on later definitions `c`, `a`', or `d` yield nothing. Each of these show up in the log like so:

```
[server] Got a method textDocument/hover
[server] processing took 0.0100135803223ms
Sending response {"id": 1949, "jsonrpc": "2.0", "result": null}
```

If I remove the extraneous later `a` definition:

```ocaml
module Foo = struct
let a b = b + b
let c d = a d
let d f = a f
end
```

…then hovers on all declarations work as expected.

Reproduce the issue with the OCaml module shown, then compare hover responses with and without the later shadowing definition. Start at the textDocument/hover request handling and trace how definitions are resolved; done means hovers on c, the later a, and d return results despite shadowing.

Written by the indexing model from the issue text.