patch 9.1.1821: filetype: Not all PKL files are recognized

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: #18271
closes: #18274

Signed-off-by: Jan Claußen <jan.claussen10@web.de>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/filetype.vim

@@ -1,7 +1,7 @@
 " Vim support file to detect file types
 "
 " Maintainer:		The Vim Project <https://github.com/vim/vim>
-" Last Change:		2025 Sep 14
+" Last Change:		2025 Oct 03
 " Former Maintainer:	Bram Moolenaar <Bram@vim.org>
 
 " Listen very carefully, I will say this only once
@@ -1971,7 +1971,7 @@ au BufNewFile,BufRead Pipfile.lock		setf json
 au BufNewFile,BufRead pixi.lock			setf yaml
 
 " Pkl
-au BufNewFile,BufRead *.pkl			setf pkl
+au BufNewFile,BufRead *.pkl,*.pcf,pkl-lsp://*	setf pkl
 
 " PL/1, PL/I
 au BufNewFile,BufRead *.pli,*.pl1		setf pli