osc: escape ASS and strip newlines on title

DOCS/man/osc.rst

@@ -244,6 +244,7 @@ Configurable Options
 
     String that supports property expansion that will be displayed as
     OSC title.
+    ASS tags are escaped, and newlines and trailing slashes are stripped.
 
 ``tooltipborder``
     Default: 1

player/lua/osc.lua

@@ -1514,6 +1514,8 @@ function osc_init()
 
     ne.content = function ()
         local title = mp.command_native({"expand-text", user_opts.title})
+        -- escape ASS, and strip newlines and trailing slashes
+        title = title:gsub("\\n", " "):gsub("\\$", ""):gsub("{","\\{")
         return not (title == "") and title or "mpv"
     end