AsYouType compilation doesn't factor in interface files

Open the `reason-react` project, and get a "variables not generalized" error on `ReasonReact.re`.

This error is legit if one deletes `ReasonReact.rei`, in which case the compiler gives the error from the command-line.

I've double checked with the other vscode extension that the error is not reported. (And that it is, if we delete `ReasonReact.rei`).

Reproduce the error in the `reason-react` project using `ReasonReact.re` with and without `ReasonReact.rei`, and compare the command-line compiler with the other VS Code extension. Then trace the language server's AsYouType compilation path to determine how interface files are handled; done means the erroneous "variables not generalized" report is absent when the interface file exists.

Written by the indexing model from the issue text.