vim-patch:9.1.1503: filetype: haxe files are not recognized

Problem:  filetype: haxe files are not recognized
Solution: detect *.hx files as haxe filetype (0xadk)

References:
- https://haxe.org/
- https://code.haxe.org/category/beginner/hello-world.html

closes: vim/vim#17644

b46e3aa0fa

Co-authored-by: 0xadk <0xadk@users.noreply.github.com>

runtime/lua/vim/filetype.lua

@@ -557,6 +557,7 @@ local extension = {
   persistentmodels = 'haskellpersistent',
   ht = 'haste',
   htpp = 'hastepreproc',
+  hx = 'haxe',
   hcl = 'hcl',
   hb = 'hb',
   h = detect.header,

test/old/testdir/test_filetype.vim

@@ -348,6 +348,7 @@ func s:GetFilenameChecks() abort
     \ 'haskellpersistent': ['file.persistentmodels'],
     \ 'haste': ['file.ht'],
     \ 'hastepreproc': ['file.htpp'],
+    \ 'haxe': ['file.hx'],
     \ 'hb': ['file.hb'],
     \ 'hcl': ['file.hcl'],
     \ 'heex': ['file.heex'],