0.10 luadoc and lsp integration

[Alexander Courtis]

0.10 adds full luadoc and function definitions for vim.*, lsp, treesitter etc.

Add these to luals:

    "library": [
      "$VIMRUNTIME/lua",
      "${3rd}/luv/library"
    ]

Resolve luals detected issues:

• type mismatches - no changes, just doc
• missing nil checks - fix
• incorrect returns/params - fix

Update documentation and function signatures to be properly typed.