The benefit of this is that users only pay for what they use. If e.g.
only `vim.lsp.buf_get_clients()` is called then they don't need to load
all modules under `vim.lsp` which could lead to significant startuptime
saving.
Also `vim.lsp.module` is a bit nicer to user compared to
`require("vim.lsp.module")`.
This isn't used for some nested modules such as `filetype` as it breaks
tests with error messages such as "attempt to index field 'detect'".
It's not entirely certain the reason for this, but it is likely it is
due to filetype being precompiled which would imply deferred loading
isn't needed for performance reasons.
Problem:
vim.treesitter does not know how to map a specific filetype to a parser.
This creates problems since in a few places (including in vim.treesitter itself), the filetype is incorrectly used in place of lang.
Solution:
Add an API to enable this:
- Add vim.treesitter.language.add() as a replacement for vim.treesitter.language.require_language().
- Optional arguments are now passed via an opts table.
- Also takes a filetype (or list of filetypes) so we can keep track of what filetypes are associated with which langs.
- Deprecated vim.treesitter.language.require_language().
- Add vim.treesitter.language.get_lang() which returns the associated lang for a given filetype.
- Add vim.treesitter.language.register() to associate filetypes to a lang without loading the parser.
