Add support for inlay hints

[baronfel]

This is most of the backend work necessary to support inlay hint display for parameter names and inferred types. It's based wholesale on @cartermp's work on dotnet/fsharp#10295.
It doesn't currently work for methods with parameters, because there's not a public version of the changes to FCS he made in that PR yet.

Next steps:

• add tests
• consider adding an inlayHint resolve method, since hints can have actions associated to them that may be difficult to perform
• consider adding an action to the type-style hints to explicitly type that expr, like we have a codeaction for already (essentially invoking that code action)

[baronfel]

I'm not going to do the resolve handler right now - we have no use case for it aside from the potential action to turn a type hint into an explicit type annotation in the code. Instead I'll log an issue as an up-for-grabs enhancement if someone wants to pick that up.