Various failures with SourceLinked files

While working on https://github.com/fsharp/FsAutoComplete/pull/1007, renaming would fail sometimes. Specifically when I went to rename an override on the LspServer, I would get an error like:

```
Could not read file: /_/src/Server.fs
```

@baronfel and I suspect it's SourceLinked files, and its trying to access the `Server.fs` file in the [LanguageServerProtocol](https://github.com/ionide/LanguageServerProtocol) project.

We should consider investigating when/where to ignore SourceLinked files. Goto Definition should support using them but Rename shouldn't, etc.