vim-patch:9.1.1821: filetype: Not all PKL files are recognized (#36008)

Problem:  filetype: Not all PKL files are recognized
Solution: Detect *.pcf as pkl filetype, detect using the pkl-lsp://
          protocol as pkl filetype, include PKL syntax script
          (Jan Claußen)

This adds basic syntax support for the new PKL language by Apple.

What works:
- Shebang support
- Comment support
- Integers (decimal, hex, octal and binary) support
- Floating point support including exponentials
- Basic datatype support
- Unicode escape delimiters
- Escape code support
- String interpolation
- Support up to five pounds for custom delimiters
- Folding of multi-line comments and blocks

What doesn't work:

  The language heavily uses parameterized type declarations, which can get
  very complex. It is very hard to highlight this properly. There is
  official Tree-sitter support for this. Since it is hard to pull this off
  in a vim syntax file, I opted for basic support of the data types.

References:
  https://github.com/apple/pkl-pantry

fixes: vim/vim#18271
closes: vim/vim#18274

67a8f2945e

Co-authored-by: Jan Claußen <jan.claussen10@web.de>

runtime/ftplugin/pkl.vim

@@ -2,13 +2,15 @@
 " Language:	Pkl
 " Maintainer:	Riley Bruins <ribru17@gmail.com>
 " Last Change:	2025 Jul 14
+" 2025 Oct 03 by Vim Project Add foldmethod #18274
 
 if exists('b:did_ftplugin')
   finish
 endif
 let b:did_ftplugin = 1
 
-setlocal comments=sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,://
+setlocal comments=sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,:///,://
 setlocal commentstring=//\ %s
+setlocal foldmethod=syntax
 
-let b:undo_ftplugin = 'setl com< cms<'
+let b:undo_ftplugin = 'setl com< cms< fdm<'