Problem: Argument type mismatches are excluded from EmmyLua checks.

Solution: Correct runtime annotations and calls, document local checker
workarounds, and enable the diagnostic.

AI-assisted

Problem:
An operator on a target that creates a Visual selection (`cgn`,
`d<C-v>j`, an omap text object like `:<C-U>normal! viw`) sets `'< '>`,
`gv` and `visualmode()` to the operator target.

This causes at least the following problems:
- clobbers the user's previous `'< '>` (annoying and usually unwanted)
  - E.g. after a custom textobj, `:help text-object-define`.
- "cgn" with a `\%V` pattern can't be dot-repeated (".")

Solution:
Don't save the Visual area if the operator target created it (operator
was pending).

Also fix `an`/`in` with `'selection'=exclusive` starting from an empty
range.

Enable checks for unused code, deprecated calls, return types, and
annotations.

Fix the warnings and replace the deprecated highlight function. Keep
exceptions where old APIs are still needed or the checker gets it wrong.

AI-assisted

Problem:
- To share logic, creating a `vim.Range` currently creates two `vim.Pos` values
  as intermediates, which causes unnecessary table allocations.
- `pos.lua` and `range.lua` contain some overlapping logic.

Solution:
Add `vim.pos._util`, a module for handling
positions represented directly by `row` and `col`.

Type fixes caught by emmylua

* refactor(docs): remove `@private` annotations from local functions

* refactor(docs): remove unnecessary `@nodoc` annotations

Problem:
treesitter injected language ranges sometimes cross over the capture
boundaries when `@combined`.

Solution:
Clip child regions to not spill out of parent regions within
languagetree.lua, and only apply highlights within those regions in
highlighter.lua.


Co-authored-by: Cormac Relf <web@cormacrelf.net>