docs(help): specify h4 "function signature" format #42434master

Work towards enabling ["flow" layout](https://github.com/neovim/neovim/blob/9244da12e400ec0291450a5e9400d995e7a29b83/src/gen/gen_help_html.lua#L86-L88)
in all `:help` files.

Problem:
The final boss of vimdoc pseudo-structure: Vim's quasi-headings on
function signatures and excmd docs is visually distinctive but too
inconsistent for a nice parse rule.

Solution:
- Define the quasi-heading format as an "h4" variant, specified at
  `:help help-tag-heading`.
  - For simplicity and predictability, it is defined as any line that
    ends with a help tag(s) preceded by 2 or more spaces (or 1 tab).
- Update existing docs.
  - This one-time update has a lot of changes, but is very unlikely to
    conflict with ported Vim-patches because (1) Vim rarely adds new
    *excmds* that we want, and (2) *function* docs are auto-generated.

ref https://github.com/neovim/tree-sitter-vimdoc/issues/110

1 files changed, 3 insertions, 3 deletions

diff --git a/runtime/doc/lua-async.txt b/runtime/doc/lua-async.txt
index e39b616799..bb77ba7909 100644
--- a/runtime/doc/lua-async.txt
+++ b/runtime/doc/lua-async.txt
@@ -98,13 +98,13 @@ task with a deadline, and `vim.async.semaphore(permits)` creates a
 section at once.
 
 
-*vim.async.Closable*
+vim.async.Closable                                        *vim.async.Closable*
 
     Fields: ~
       • {close}        (`fun(self, callback?: fun())`)
       • {is_closing}?  (`fun(self): boolean`)
 
-*vim.async.Semaphore*
+vim.async.Semaphore                                      *vim.async.Semaphore*
     A semaphore manages an internal permit counter. |Semaphore:acquire()|
     consumes one permit and |Semaphore:release()| returns one permit. If no
     permits are available, `acquire()` suspends the current task until another
@@ -147,7 +147,7 @@ section at once.
       • {with}     (`fun(self: vim.async.Semaphore, fn: async fun(): R...): R...`)
                    See |Semaphore:with()|.
 
-*vim.async.Task*
+vim.async.Task                                                *vim.async.Task*
     Extends: |vim.async.Closable|
 
     A coroutine-backed async operation and concurrency scope.