**Problem:** `vim.treesitter.get_parser()` and `vim.treesitter.start()`
both parse the tree before returning it. This is problematic because if
this is a sync parse, it will stall the editor on large files. If it is
an async parse, the functions return stale trees.

**Solution:** Remove this parsing side effect and leave it to the user
to parse the returned trees, either synchronously or asynchronously.

**Problem:** Parsing can be slow for large files, and it is a blocking
operation which can be disruptive and annoying.

**Solution:** Provide a function for asynchronous parsing, which accepts
a callback to be run after parsing completes.

Co-authored-by: Lewis Russell <lewis6991@gmail.com>
Co-authored-by: Luuk van Baal <luukvbaal@gmail.com>
Co-authored-by: VanaIgr <vanaigranov@gmail.com>

**Problem:** Currently, it is difficult to get node(s)-level metadata
for a capture returned by `get_captures_at_pos()`. This is because it is
stored in `metadata[id]` and we do not have access to the value of `id`,
so to get this value we have to iterate over the keys of `metadata`. See
[this commit](https://github.com/neovim/neovim/commit/d63622930001b39b12f14112fc3abb55b760c447#diff-8bd4742121c2f359d0345f3c6c253a58220f1a28670cc4e1c957992232059a6cR16).

Things would be much simpler if we were given the `id` of the capture so
we could use it to just index `metadata` directly.

**Solution:** Include `id` in the data returned by
`get_captures_at_pos()`

Problem:

`vim.validate()` takes two forms when it only needs one.

Solution:

- Teach the fast form all the features of the spec form.
- Deprecate the spec form.
- General optimizations for both forms.
- Add a `message` argument which can be used alongside or in place
  of the `optional` argument.

- Also fix `vim.validate()` for PUC Lua when showing errors for values
  that aren't string or number.

This commit also marks `child_containing_descendant()` as deprecated
(per upstream's documentation), and uses `child_with_descendant()` in
its place. Minimum required tree-sitter version will now be `0.24`.

An implication of this current approach is that `NVIM_API_LEVEL` should be
bumped when a new Lua function is added.

TODO(future): add a lint check which requires `@since` on all new functions.

ref #25416