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/lua/vim/_meta/options.lua

@@ -3834,20 +3834,27 @@ vim.go.keymodel = vim.o.keymodel
 vim.go.km = vim.go.keymodel
 
 --- Program to use for the `K` command.  Environment variables are
---- expanded `:set_env`.  ":help" may be used to access the Vim internal
---- help.  (Note that previously setting the global option to the empty
---- value did this, which is now deprecated.)
---- When the first character is ":", the command is invoked as a Vim
---- Ex command prefixed with [count].
---- When "man" or "man -s" is used, Vim will automatically translate
---- a [count] for the "K" command to a section number.
+--- expanded `:set_env`.
+---
+--- Special cases:
+--- - ":help" opens the `word` at cursor using `:help`.  (Note that
+---   previously setting the global option to the empty value did this,
+---   which is now deprecated.)
+--- - ":help!" performs `:help!` (DWIM) on the `WORD` at cursor.
+--- - If the value starts with ":", it is invoked as an Ex command
+---   prefixed with [count].
+--- - If "man" or "man -s", [count] is the manpage section number.
+---
 --- See `option-backslash` about including spaces and backslashes.
+---
 --- Example:
 ---
 --- ```vim
+--- 	set keywordprg=:help!
 --- 	set keywordprg=man\ -s
 --- 	set keywordprg=:Man
 --- ```
+---
 --- This option cannot be set from a `modeline` or in the `sandbox`, for
 --- security reasons.
 ---