vim-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: vim/vim#18027

0c4405a6b2

Co-authored-by: WuJunkai2004 <wujunkai20041123@outlook.com>

runtime/lua/vim/filetype.lua

@@ -278,6 +278,7 @@ local extension = {
   c3t = 'c3',
   cabal = 'cabal',
   cairo = 'cairo',
+  cj = 'cangjie',
   capnp = 'capnp',
   cdc = 'cdc',
   cdl = 'cdl',