patch 9.1.0386: filetype: stylus files not recognized

Problem:  filetype: stylus files not recognized
Solution: Detect '*.styl' and '*.stylus' as stylus filetype,
          include indent, filetype and syntax plugin
          (Philip H)

closes: #14656

Signed-off-by: Philip H <47042125+pheiduck@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/stylus.vim

@@ -0,0 +1,54 @@
+" Vim filetype plugin
+" Language: Stylus
+" Maintainer: Marc Harter
+" Credits: Tim Pope
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+
+let s:save_cpo = &cpo
+set cpo-=C
+
+" Define some defaults in case the included ftplugins don't set them.
+let s:undo_ftplugin = ""
+let s:browsefilter = "All Files (*.*)\t*.*\n"
+
+runtime! ftplugin/html.vim ftplugin/html_*.vim ftplugin/html/*.vim
+unlet! b:did_ftplugin
+
+" Override our defaults if these were set by an included ftplugin.
+if exists("b:undo_ftplugin")
+  let s:undo_ftplugin = b:undo_ftplugin
+  unlet b:undo_ftplugin
+endif
+if exists("b:browsefilter")
+  let s:browsefilter = b:browsefilter
+  unlet b:browsefilter
+endif
+
+" Change the browse dialog on Win32 to show mainly Styl-related files
+if has("gui_win32")
+  let b:browsefilter="Stylus Files (*.styl)\t*.styl\n" . s:browsefilter
+endif
+
+setlocal comments= commentstring=//\ %s
+setlocal suffixesadd=.styl
+setlocal formatoptions+=r
+
+" Add '-' and '#' to the what makes up a keyword.
+" This means that 'e' and 'w' work properly now, for properties
+" and valid variable names.
+setl iskeyword+=#,-
+
+" Add a Stylus command (to see if it's valid)
+command -buffer Stylus !clear; cat % |stylus
+
+
+let b:undo_ftplugin = "setl sua< isk< cms< com< fo< "
+      \ " | unlet! b:browsefilter b:match_words | " . s:undo_ftplugin
+
+let &cpo = s:save_cpo
+
+" vim:set sw=2: