runtime(yara): add ftplugin for yara filetype

Add a minimal ftplugin `runtime/ftplugin/yara.vim` that sets:
- `commentstring` for YARA line comments (`//`)
- `comments` for YARA block comment (`/* */`)
- `formatoptions` to wrap comment lines and continue comment after newlines
This was heavily inspired from `runtime/ftplugin/c.vim`

closes: #19736

Signed-off-by: Thomas Dupuy <thom4s.d@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/yara.vim

@@ -0,0 +1,22 @@
+" Vim filetype plugin file
+" Language: YARA
+" Maintainer: The Vim Project <https://github.com/vim/vim>
+" Last Change: 2026 Mar 17
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+
+" Don't load another plugin for this buffer
+let b:did_ftplugin = 1
+
+" Set 'formatoptions' to break comment lines but not other lines,
+" and insert the comment leader when hitting <CR> or using "o".
+setlocal formatoptions-=t formatoptions+=croql
+
+setlocal commentstring=//\ %s
+setlocal comments=s1:/*,mb:*,ex:*/,://
+
+" Undo settings when leaving buffer
+let b:undo_ftplugin = "setlocal commentstring< comments< formatoptions<"