[css-text-3] Trim trailing OGHAM SPACE MARK per UAX14.

Author: fantasai

css-text-3/Overview.bs

@@ -1552,7 +1552,9 @@ Text Processing</h3>
 
       <li>A sequence at the end of a line
         of <a>collapsible</a> [=spaces=]
-        is removed.
+        is removed,
+        and any trailing U+1680 OGHAM SPACE MARK
+        is also removed.
 
         <wpt>
           white-space/line-edge-white-space-collapse-001.html