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.
Problem: Some injections (like markdown) allow specifying arbitrary
language names for code blocks, which may be lead to errors when
looking for a corresponding parser in runtime path.
Solution: Validate that the language name only contains alphanumeric
characters and `_` (e.g., for `c_sharp`) and error otherwise.
