Added empty appendix with id=bold-script-mappings

There are still tests on WPT that refer to this appendix. Leaving an empty appendix is a temporary solution until the tests have been deleted.

spec.html

@@ -5926,6 +5926,9 @@ <h3 id="new-text-transform-mappings">Mathematical Alphanumeric Symbols</h3>
         <h4><code>italic</code> mappings</h4>
         <div data-include="tables/mathvariants-italic.html"></div>
       </section>
+      <section class="informative" id="bold-script-mappings">
+        <h4>This appendix has been removed.</h4>
+      </section>
       <section class="informative" id="bold-italic-mappings">
         <h4>This appendix has been removed.</h4>
       </section>