closes #24141
closes #24746

Support Markdown code blocks in addition to <pre> blocks in Doxygen doc
comments.

Update doc comments in iter.lua as a test.

If an iterator pipeline stage returns nil as its first return value, the
other return values are ignored and it is treated as if that stage
returned only nil (the semantics of returning nil are different between
different stages). This is consistent with how for loops work in Lua
more generally, where the for loop breaks when the first return value
from the function iterator is nil (see :h for-in for details).

Co-authored-by: Kevin Pham <keevan.pham@gmail.com>

* docs(lua): teach lua2dox how to table

* docs(lua): teach gen_vimdoc.py about local functions

No more need to mark local functions with @private

* docs(lua): mention @nodoc and @meta in dev-lua-doc

* fixup!

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

---------

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

gen_help_html: truncate parse-error sample text

Co-authored by: zeertzjq <zeertzjq@outlook.com>
Co-authored by: Steven Todd McIntyre II <114119064+stmii@users.noreply.github.com>
Co-authored by: nobe4 <nobe4@users.noreply.github.com>

- docs: mention --luadev-mod to run with lua runtime files
  When changing a lua file in the ./runtime folder, a new contributor
  might expect changes to be applied to the built Neovim binary.

A table passed to `vim.iter` can be a class instance with a `__call`
implementation for the iterator protocol.