Simple completion in type hints/definitions

[tboby]

This adds a simple, flawed, but nevertheless useful, filter to completion results when the location is inside a SynType. This works in record fields and type hints. I haven't checked exhaustively, but I trust the AST walker and unless I've misunderstood we shouldn't find general expressions inside.

I tried to use this for Type parameters but it didn't work. I'm not very familiar with FCS's internals but I suspect it only uses getAllSymbols as a fallback and so doesn't need it in type pars. I imagine this means this feature will stop working with some future update of FCS.

This feature still suffers from the problem of the first few characters not triggering completion correctly.

Completion in a record field's type:

Completion in a normal expression:

Completion in a type hint:

Q: Are there any other completion items that should be returned? Keywords?

[baronfel]

This is a good usability fix, and something we can build on 👍