Initial InlayHint provider implementation

[pfitzseb]

Todo:

• [ ] better method selection
• [x] better tooltips
• [x] take request range into account
• [x] get rid of hints in func defs
• [x] settings
  • [x] none
  • [x] all
  • [x] literals only
• [x] tests

[pfitzseb]

[fredrikekre]

settings

Perhaps it would be useful to have constructors as a setting? Personally I am not sure how useful hints would be for general functions, since the argument names are like an implementation detail, but when you construct something I still think it would be useful. For example: https://github.com/julia-vscode/LanguageServer.jl/blob/5b4e8e87b5fdb8afac826f4179237bca3987a0b6/src/languageserverinstance.jl#L67-L94

[chriselrod]

I'm a fan of this feature in C++, looking forward to having it in Julia!

[Zentrik]

I rebased this onto master here, https://github.com/Zentrik/LanguageServer.jl/tree/inlay-hints.

[ParadaCarleton]

This would be amazing to have--any more progress?