refactor(treesitter): remove nvim-treesitter dependencies

[wookayin]

Replace all the use of nvim-treesitter APIs with core vim.treesitter APIs. No more nvim-treesitter dependency, just core neovim is enough.

This fix makes ufo work without the nvim-treesitter plugin as an additional dependency. In fact, nvim-treesitter v1.0 deprecates and removes some APIs that have been migrated to the core neovim APIs vim.treesitter, which makes ufo's previous treesitter provider implementation incompatible.

Note that this commit does not change the minimum neovim version requirement, should work fine with neovim 0.7.x.

Implementation note:

There are four APIs that need to be migrated:

• nvim-treesitter.parsers.get_parser(): The difference to the core API vim.treesitter.get_parser() is whether to throw errors when a parser is not available (has_parser). We simply mimic the previous behavior by catching errors.

• nvim-treesitter.query.get_query(): The difference to core API vim.treesitter.query.get() is whether the query file is cached or not. This may have a small performance impact; in neovim 0.10.x, this function is memoized and thus very fast, but in neovim <= 0.9.x it might be slightly slow due to the lack of cache.

  Note: One can consider as well automatically falling back to the old nvim-treesitter (v0.9.x) if available, for neovim < 0.10.

• nvim-treesitter.query.has_folds() (i.e., has_query_files()): can be easily replaced with vim.treesitter.query.get_files. Also there might be a subtle performance difference of whether cache is being used (in the old nvim-treesitter implementations) or not.

• nvim-treesitter.tsrange: The TSRange API has gone. Note that this is used only to implement the #make-range! directive; it suffices to have node:range() only for where it's used. Therefore, TSRange.from_nodes() is the only API we'll need, which can be easily backported into the existing MetaNode implementation.