feat: adds type hierarchy request support

[karthiknadig]

Description (e.g. "Related to ...", etc.)

Adds type hierarchy request support

Code review checklist (for code reviewer to complete)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Commit messages are meaningful (see this for details)
• Tests have been included and/or updated, as appropriate
• Docstrings have been included and/or updated, as appropriate
• Standalone docs have been updated accordingly

[tombh]

This is still marked as "draft", so there's still some things to add?

Not that you need to change the tests, but I think the tests here could take advantage of the new LanguageClient that @alcarney has added. See here for an example. Like I say, you don't need to change the tests, it's just so you're aware.

[karthiknadig]

@tombh I had kept is as draft because I was making sure my tests pass.

[tombh]

🚀