vim-patch:9.1.1042: filetype: just files are not recognized

Problem:  filetype: just files are not recognized
Solution: adjust filetype detection pattern, detect just shebang line,
          include just ftplugin, indent and syntax plugin
          (Peter Benjamin)

closes: vim/vim#16466

72755b3c8e

Co-authored-by: Peter Benjamin <petermbenjamin@gmail.com>

runtime/ftplugin/just.vim

@@ -0,0 +1,17 @@
+" Vim ftplugin file
+" Language:	Justfile
+" Maintainer:	Peter Benjamin <@pbnj>
+" Last Change:	2025 Jan 19
+" Credits:	The original author, Noah Bogart <https://github.com/NoahTheDuke/vim-just/>
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal iskeyword+=-
+setlocal comments=n:#
+setlocal commentstring=#\ %s
+
+let b:undo_ftplugin = "setlocal iskeyword< comments< commentstring<"