vim-patch:9.1.0425: filetype: purescript files are not recognized

Problem:  filetype: purescript files are not recognized
Solution: recognize '*.purs' files as purescript filetype,
          include basic purescript filetype plugin
          (Riley Bruins)

Reference: https://github.com/purescript/documentation/blob/master/language/Syntax.md#comments

closes: vim/vim#14813

155583a5c3

Co-authored-by: Riley Bruins <ribru17@hotmail.com>

runtime/ftplugin/purescript.vim

@@ -0,0 +1,14 @@
+" Vim filetype plugin
+" Language:	purescript
+" Maintainer:	Riley Bruins <ribru17@gmail.com>
+" Last Change:	2024 May 19
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setl comments=s1f:{-,mb:\ ,ex:-},:--\ \|,:--
+setl commentstring=--\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'

runtime/lua/vim/filetype.lua

@@ -845,6 +845,7 @@ local extension = {
   psf = 'psf',
   psl = 'psl',
   pug = 'pug',
+  purs = 'purescript',
   arr = 'pyret',
   pxd = 'pyrex',
   pyx = 'pyrex',

test/old/testdir/test_filetype.vim

@@ -578,6 +578,7 @@ func s:GetFilenameChecks() abort
     \ 'psl': ['file.psl'],
     \ 'pug': ['file.pug'],
     \ 'puppet': ['file.pp'],
+    \ 'purescript': ['file.purs'],
     \ 'pymanifest': ['MANIFEST.in'],
     \ 'pyret': ['file.arr'],
     \ 'pyrex': ['file.pyx', 'file.pxd'],