feat(help): super K (":help!") guesses tag at cursor #36205

Problem:
`K` in help files may fail in some noisy text. Example:

      (`fun(config: vim.lsp.ClientConfig): boolean`)
                            ^cursor

Solution:
- `:help!` (bang, no args) activates DWIM behavior: tries `<cWORD>`,
  then trims punctuation until a valid tag is found.
- Set `keywordprg=:help!` by default.
- Does not affect `CTRL-]`, that is still fully "tags" based.

runtime/ftplugin/help.vim

@@ -17,7 +17,7 @@ let b:undo_ftplugin = "setl isk< fo< tw< cole< cocu< keywordprg< omnifunc< comme
 
 setl comments= cms=
 
-setlocal formatoptions+=tcroql textwidth=78 keywordprg=:help omnifunc=s:HelpComplete
+setlocal formatoptions+=tcroql textwidth=78 keywordprg=:help! omnifunc=s:HelpComplete
 let &l:iskeyword='!-~,^*,^|,^",192-255'
 if has("conceal")
   setlocal cole=2 cocu=nc