Replace InlayHints with official provider

[adam-fowler]

VSCode 1.65 introduces the official Inlay hints provider
https://code.visualstudio.com/updates/v1_65#_inlay-hints

Currently need to construct an inlay hint provider using the InlayHintsRequest setup in the extension

Could wait on support from vscode-languageclient/node, but don't know how long that'll take