Work towards enabling "flow" layout in most `:help` files.

Since [tables are supported in help](https://github.com/neovim/tree-sitter-vimdoc#tables),
it's now possible to render most help files as ["flow" layout](https://github.com/neovim/neovim/blob/9244da12e400ec0291450a5e9400d995e7a29b83/src/gen/gen_help_html.lua#L86-L88)
instead of the legacy fixed-width layout. Besides [improved HTML rendering](https://github.com/neovim/neovim/pull/42381#discussion_r4285705739),
flow layout will allow `:help` presentation-mode to un-hardwrap text
blocks.

Work towards enabling "flow" layout in most `:help` files.

Since [tables are supported in help](https://github.com/neovim/tree-sitter-vimdoc#tables),
it's now possible to render most help files as ["flow" layout](https://github.com/neovim/neovim/blob/9244da12e400ec0291450a5e9400d995e7a29b83/src/gen/gen_help_html.lua#L86-L88)
instead of the legacy fixed-width layout. Besides [improved HTML rendering](https://github.com/neovim/neovim/pull/42381#discussion_r4285705739),
flow layout will allow `:help` presentation-mode to un-hardwrap text
blocks.

Work towards enabling "flow" layout in most `:help` files.

Since [tables are supported in
help](https://github.com/neovim/tree-sitter-vimdoc#tables), it's now possible to
render most help files as ["flow" layout](https://github.com/neovim/neovim/blob/9244da12e400ec0291450a5e9400d995e7a29b83/src/gen/gen_help_html.lua#L86-L88)
instead of the legacy fixed-width layout. Besides [improved HTML rendering](https://github.com/neovim/neovim/pull/42381#discussion_r4285705739),
flow layout will allow `:help` presentation-mode to un-hardwrap text blocks.
https://github.com/neovim/neovim/issues/31825

highlights.scm: `#match` is slow, prefer `#lua-match`.

Problem:
- `<` before a listitem (`< - foo`) is not concealed.
- Codeblock HTML has extra blank lines.
- Codeblock in a listitem ends the listitem, so HTML docs drop the rest
  of the item and its nesting. Example from `:h nvim_open_win()`:
  ```
        • border: … the double-box style can be specified as: >
          [ "╔", "═" ,"╗", "║", "╝", "═", "╚", "║" ].
    <
          If fewer than eight chars are given, they will be repeated.
        • bufpos: …

    tree-sitter-vimdoc v4.1.0:
      (block
        (line_li (prefix) (line) (codeblock (code (line)))))
      (block
        (line)                                  ; "If fewer…"
        (line_li (prefix) (line) (line)))       ; "bufpos"

    tree-sitter-vimdoc v4.2.0:
      (block
        (line_li (prefix) (line) (codeblock (code (line)))
          (line))                               ; "If fewer…"
        (line_li (prefix) (line) (line)))       ; "bufpos"
  ```

Solution:
- Bump tree-sitter-vimdoc to v4.2.0. https://github.com/neovim/tree-sitter-vimdoc/pull/174
- gen_help_html: get listitem indent from its first line
- gen_help_html: don't double codeblock newlines.
- highlight query: conceal `<` in `line_li`.
- docs: fix doc sources where a blank line was missing after listitems
  followed by non-listitem text.

Problem: vim.fn.getloclist() is untyped, unlike getqflist().

Solution: Split it into typed list and {what} forms, like getqflist().

closes: vim/vim#21361

https://github.com/vim/vim/commit/5959274607038bac22e9dde740060ddb748fedfe

Omit :h :source-dryrun as it needs changes to port to Nvim anyway.

Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>

closes: vim/vim#21362

https://github.com/vim/vim/commit/b3a4882a915634c6031a4b4c8e25d459ac7b4319

The expand() overload required nosuf even though callers can pass nil.
Mark it optional in the source metadata and regenerate the Lua types.

AI-assisted