[css-text-3] Don't export unqualified 'collapsible' as a term

Author: fantasai

css-text-3/Overview.bs

@@ -1303,7 +1303,7 @@ Text Processing</h3>
     <ul>
     <li id="collapse"><p>If 'white-space' is set to
       ''white-space/normal'', ''nowrap'', or ''pre-line'',
-      [=white space characters=] are considered <dfn export lt="collapsible white space|collapsible">collapsible</dfn>
+      [=white space characters=] are considered <dfn export lt="collapsible white space" local-lt="collapsible">collapsible</dfn>
       and are processed by performing the following steps:</p>
       <ol>
         <li>Any sequence of collapsible [=spaces=] and [=tabs=]