runtime(vim): Update help syntax file, improve highlighting of included Vim examples

- Take over as file maintainer.
- Improve highlighting of legacy script examples by using :syn-iskeyword
  with the default 'iskeyword' value. Vim9 script examples are not
  supported yet.
- Match admonition labels in more contexts.
- Match URLs in more contexts.

fixes #17721
closes: #17731

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/eval.txt

@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 9.1.  Last change: 2025 Jun 28
+*eval.txt*	For Vim version 9.1.  Last change: 2025 Jul 13
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5210,7 +5210,7 @@ The |:Launch| user command uses shell completion for its first argument.
 
 NOTE: escaping of <args> is left to the user
 
-Examples: >vim
+Examples: >
 	vim9script
 
 	import autoload 'dist/vim9.vim'

runtime/doc/fold.txt

@@ -1,4 +1,4 @@
-*fold.txt*      For Vim version 9.1.  Last change: 2025 Jul 09
+*fold.txt*      For Vim version 9.1.  Last change: 2025 Jul 13
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -164,7 +164,7 @@ level is found.
 If this proves difficult, the next best thing could be to cache all fold
 levels in a buffer-local variable (b:foldlevels) that is only updated on
 |b:changedtick|:
->vim
+>
   vim9script
   def MyFoldFunc(): number
     if b:lasttick == b:changedtick

runtime/doc/usr_25.txt

@@ -1,4 +1,4 @@
-*usr_25.txt*	For Vim version 9.1.  Last change: 2025 Jun 10
+*usr_25.txt*	For Vim version 9.1.  Last change: 2025 Jun 13
 
 		     VIM USER MANUAL - by Bram Moolenaar
 
@@ -200,7 +200,7 @@ command: >vim
 
 Or put this line in your |vimrc|: >vim
 
-	packadd! justify
+	:packadd! justify
 
 This Vim script file defines a new visual command "_j".  To justify a block of
 text, highlight the text in Visual mode and then execute "_j".