patch 9.1.1647: filetype: Cangjie files are not recognized

Problem:  filetype: Cangjie files are not recognized
Solution: Detect *.cj files as cangjie filetype, include a syntax plugin
          (WuJunkai2004)

This commit introduces a new syntax highlighting file for the Cangjie
programming language, includes 4 parts as required:
- The main syntax file: runtime/syntax/cangjie.vim
- The filetype detection rule in: runtime/filetype.vim
- The documentation update in: runtime/doc/syntax.txt
- Some menus

References:
- https://gitcode.com/Cangjie
- https://cangjie-lang.cn/

fixes: 18014
closes: #18027

Signed-off-by: WuJunkai2004 <wujunkai20041123@outlook.com>
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/syntax.txt

@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2025 Aug 10
+*syntax.txt*	For Vim version 9.1.  Last change: 2025 Aug 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -1116,6 +1116,23 @@ in the "after" directory in 'runtimepath'.  For Unix this would be
     syn sync fromstart
     set foldmethod=syntax
 
+CANGJIE					*cangjie.vim* *ft-cangjie-syntax*
+
+This file provides syntax highlighting for the Cangjie programming language, a
+new-generation language oriented to full-scenario intelligence.
+
+All highlighting is enabled by default.  To disable highlighting for a
+specific group, set the corresponding variable to 0 in your |vimrc|.
+All options to disable highlighting are: >
+	:let g:cangjie_comment_color = 0
+	:let g:cangjie_identifier_color = 0
+	:let g:cangjie_keyword_color = 0
+	:let g:cangjie_macro_color = 0
+	:let g:cangjie_number_color = 0
+	:let g:cangjie_operator_color = 0
+	:let g:cangjie_string_color = 0
+	:let g:cangjie_type_color = 0
+
 CH						*ch.vim* *ft-ch-syntax*
 
 C/C++ interpreter.  Ch has similar syntax highlighting to C and builds upon

runtime/doc/tags

@@ -6486,6 +6486,7 @@ c_space_errors	syntax.txt	/*c_space_errors*
 c_syntax_for_h	syntax.txt	/*c_syntax_for_h*
 c_wildchar	cmdline.txt	/*c_wildchar*
 call()	builtin.txt	/*call()*
+cangjie.vim	syntax.txt	/*cangjie.vim*
 carriage-return	intro.txt	/*carriage-return*
 case	change.txt	/*case*
 catch-all	eval.txt	/*catch-all*
@@ -7424,6 +7425,7 @@ ft-bash-syntax	syntax.txt	/*ft-bash-syntax*
 ft-basic-syntax	syntax.txt	/*ft-basic-syntax*
 ft-c-omni	insert.txt	/*ft-c-omni*
 ft-c-syntax	syntax.txt	/*ft-c-syntax*
+ft-cangjie-syntax	syntax.txt	/*ft-cangjie-syntax*
 ft-ch-syntax	syntax.txt	/*ft-ch-syntax*
 ft-changelog-plugin	filetype.txt	/*ft-changelog-plugin*
 ft-changelog-syntax	syntax.txt	/*ft-changelog-syntax*