vim-patch:9.0.2062: Janet files are not recognised

Problem:  Janet files are not recognised
Solution: Add filename and shebang detection (without
          adding an extra filetype plugin)

Those are used by the Janet language:
http://www.janet-lang.org

closes: vim/vim#13400

c038427d2a

Co-authored-by: Doug Kearns <dougkearns@gmail.com>

runtime/lua/vim/filetype.lua

@@ -536,6 +536,7 @@ local extension = {
   jal = 'jal',
   jpr = 'jam',
   jpl = 'jam',
+  janet = 'janet',
   jav = 'java',
   java = 'java',
   jj = 'javacc',

runtime/lua/vim/filetype/detect.lua

@@ -1652,8 +1652,9 @@ local patterns_hashbang = {
   ['icon\\>'] = { 'icon', { vim_regex = true } },
   guile = 'scheme',
   ['nix%-shell'] = 'nix',
-  ['crystal\\>'] = { 'crystal', { vim_regex = true } },
+  ['^crystal\\>'] = { 'crystal', { vim_regex = true } },
   ['^\\%(rexx\\|regina\\)\\>'] = { 'rexx', { vim_regex = true } },
+  ['^janet\\>'] = { 'janet', { vim_regex = true } },
 }
 
 ---@private

test/old/testdir/test_filetype.vim

@@ -325,6 +325,7 @@ func s:GetFilenameChecks() abort
     \ 'j': ['file.ijs'],
     \ 'jal': ['file.jal', 'file.JAL'],
     \ 'jam': ['file.jpl', 'file.jpr', 'JAM-file.file', 'JAM.file', 'Prl-file.file', 'Prl.file'],
+    \ 'janet': ['file.janet'],
     \ 'java': ['file.java', 'file.jav'],
     \ 'javacc': ['file.jj', 'file.jjt'],
     \ 'javascript': ['file.js', 'file.jsm', 'file.javascript', 'file.es', 'file.mjs', 'file.cjs'],
@@ -864,6 +865,7 @@ let s:script_checks = {
       \ 'crystal': [['#!/path/crystal']],
       \ 'rexx': [['#!/path/rexx'],
       \          ['#!/path/regina']],
+      \ 'janet': [['#!/path/janet']],
       \ }
 
 " Various forms of "env" optional arguments.