Support for registerCapability for formatting and rangeFormatting

[adrian-budau]

Rudimentary support is quite easy to implement (ignoring document filters) and would fix most of the language servers based on vscode-languageserver-node that seem to only support formatting and rangeFormatting only as dynamic capability, without helix advertising support for it.

I've implemented this level of support on a personal branch and I'd be happy to open a PR but I'm waiting on a different PR to land in lsp-types #280

[kirawi]

The range formatting part is a dupe of #3209

[kirawi]

registerCapability is a dupe of #5141

[pascalkuthe]

Also I am pretty sure that I used language servers baswd on vscode-languahe-server bide where formatting was working so I am not sure that is generally true.

I would prefer to not add dynamic capability registration. It's not really useful to us and a spec compliant server should allow static registration