patch 9.1.0839: filetype: leo files are not recognized

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

References:
https://github.com/ProvableHQ/leo

closes: #15988

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

.github/MAINTAINERS

@@ -202,6 +202,7 @@ runtime/ftplugin/kdl.vim		@imsnif @jiangyinzuo
 runtime/ftplugin/kivy.vim		@ribru17
 runtime/ftplugin/kotlin.vim		@udalov
 runtime/ftplugin/ldapconf.vim		@ribru17
+runtime/ftplugin/leo.vim		@ribru17
 runtime/ftplugin/less.vim		@genoma
 runtime/ftplugin/lex.vim		@ribru17
 runtime/ftplugin/liquid.vim		@tpope

runtime/filetype.vim

@@ -1325,6 +1325,9 @@ au BufRead,BufNewFile *.ldg,*.ledger,*.journal			setf ledger
 " lf configuration (lfrc)
 au BufNewFile,BufRead lfrc			setf lf
 
+" Leo
+au BufNewFile,BufRead *.leo			setf leo
+
 " Less
 au BufNewFile,BufRead *.less			setf less
 

runtime/ftplugin/leo.vim

@@ -0,0 +1,13 @@
+" Vim filetype plugin
+" Language:	Leo
+" Maintainer:	Riley Bruins <ribru17@gmail.com>
+" Last Change:	2024 Nov 03
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setl comments=:// commentstring=//\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'

src/testdir/test_filetype.vim

@@ -408,6 +408,7 @@ def s:GetFilenameChecks(): dict<list<string>>
     ldif: ['file.ldif'],
     lean: ['file.lean'],
     ledger: ['file.ldg', 'file.ledger', 'file.journal'],
+    leo: ['file.leo'],
     less: ['file.less'],
     lex: ['file.lex', 'file.l', 'file.lxx', 'file.l++'],
     lf: ['lfrc'],

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    839,
 /**/
     838,
 /**/