patch 9.1.0424: filetype: slint files are not recognized

Problem:  filetype: slint files are not recognized
Solution: Detect '*.slint' files as slint filetype,
          include basic sling filetype plugin
          (Riley Bruins)

closes: #14808

Signed-off-by: Riley Bruins <ribru17@hotmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/slint.vim b/runtime/ftplugin/slint.vim
new file mode 100644
index 0000000..ac8057f
--- /dev/null
+++ b/runtime/ftplugin/slint.vim
@@ -0,0 +1,15 @@
+" Vim filetype plugin
+" Language:	slint
+" Maintainer:	Riley Bruins <ribru17@gmail.com>
+" Last Change:	2024 May 19
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+" Set 'comments' to format dashed lists in comments.
+" Also include ///, used for Doxygen.
+setl comments=sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,:///,:// commentstring=//\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'