Use DOMString for internal data of Trusted Types (#37472)

This avoids various conversions back and forth between DOMString and
String. By using DOMString consistently, we avoid these
double-conversions. The only caveat are the USVString which are
initially passed into
TrustedScriptURL.

Part of #36258

Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>

components/script/dom/document.rs

@@ -3783,7 +3783,9 @@ impl Document {
                 containing_class,
                 field,
                 can_gc,
-            )?;
+            )?
+            .as_ref()
+            .to_owned();
         }
         // Step 5: If lineFeed is true, append U+000A LINE FEED to string.
         if line_feed {