Enable initial r support

[BlueDrink9]

I'm still wrapping my head around treesitter to add the supported scopes, so I'll update this PR and add relevant tests once I do + once the r PR is added to vscode's parse tree

Checklist

• I have added tests
• I have updated the docs and cheatsheet
• I have not broken the cheatsheet

[BlueDrink9]

I'm marking this as ready to make adding scopes easier. Once r support is included in cursorless, it will be easier for it to pick it up as an option for adding scopes

[AndreasArvidsson]

Latest version of the parse tree is published and should be available in the marketplace very soon.

[BlueDrink9]

@AndreasArvidsson ready to review! Thank you again for your help yesterday

[AndreasArvidsson]

Please add a scope test for an empty argument list as well. The difference is the insertion delimiter. Please have a look at how it's implemented in other languages.

[AndreasArvidsson]

I would recommend that you create multiple scope files for the same facet instead of adding multiple different code examples in the same file. It's much simpler to review it that way.

[AndreasArvidsson]

Looks like you're starting to get the hang of this :)

• Might be worth adding a test for a vertical argument list for both argument.actual and argumentList.formal.
• Looks like you're still missing argument.formal
• Don't forget to add iteration scopes for argument otherwise you can't do every arg

[AndreasArvidsson]

@BlueDrink9 Regarding iteration domain for arguments
#2930