patch 9.1.0826: filetype: sway files are not recognized

Problem:  filetype: sway files are not recognized
Solution: detect '*.sw' files as sway filetype, include
          a filetype plugin (Riley Bruins)

References:
 https://github.com/FuelLabs/sway.

Comments taken from their syntax documentation. File extension taken
from the same documentation/GitHub's own recognition of these file types

closes: #15973

Signed-off-by: Riley Bruins <ribru17@hotmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/sway.vim

@@ -0,0 +1,15 @@
+" Vim filetype plugin
+" Language:	Sway
+" Maintainer:	Riley Bruins <ribru17@gmail.com>
+" Last Change:	2024 Nov 01
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setl commentstring=//\ %s
+" From Rust comments
+setl comments=s0:/*!,ex:*/,s1:/*,mb:*,ex:*/,:///,://!,://
+
+let b:undo_ftplugin = 'setl com< cms<'