runtime(vim): Update syntax and ftplugin files (#13924)

Improve matching of line-continuations and interspersed comments.

These are now also matched in multiline syntax command patterns,
dictionary literals, and parenthesised expressions and argument lists.

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/vim.vim b/runtime/ftplugin/vim.vim
index 1d340e4..575af74 100644
--- a/runtime/ftplugin/vim.vim
+++ b/runtime/ftplugin/vim.vim
@@ -58,7 +58,7 @@
 
 " Set 'comments' to format dashed lists in comments, both in Vim9 and legacy
 " script.
-setlocal com=sO:#\ -,mO:#\ \ ,eO:##,:#,sO:\"\ -,mO:\"\ \ ,eO:\"\",:\"
+setlocal com=sO:#\ -,mO:#\ \ ,eO:##,:#\\\ ,:#,sO:\"\ -,mO:\"\ \ ,eO:\"\",:\"\\\ ,:\"
 
 " set 'include' to recognize import commands
 setlocal include=\\v^\\s*import\\s*(autoload)?