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/makemenu.vim

@@ -124,6 +124,7 @@ SynMenu C.C++:cpp
 SynMenu C.C#:cs
 SynMenu C.Cabal\ Haskell\ build\ file:cabal
 SynMenu C.Calendar:calendar
+SynMenu C.Cangjie:cangjie
 SynMenu C.Cascading\ Style\ Sheets:css
 SynMenu C.CDL:cdl
 SynMenu C.Cdrdao\ TOC:cdrtoc