[dart:html] Add firefox to requestFullscreen's SupportedBrowsers

Change-Id: I13f9db6a8d4a8d8ae1e17604db075120e0470dd4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/229941
Auto-Submit: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Riley Porter <rileyporter@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>

sdk/lib/html/dart2js/html_dart2js.dart

@@ -14000,6 +14000,7 @@ class Element extends Node
    * * [Fullscreen specification](http://www.w3.org/TR/fullscreen/) from W3C.
    */
   @SupportedBrowser(SupportedBrowser.CHROME)
+  @SupportedBrowser(SupportedBrowser.FIREFOX)
   @SupportedBrowser(SupportedBrowser.SAFARI)
   Future<void> requestFullscreen([Map? options]) {
     var retValue;

tools/dom/templates/html/impl/impl_Element.darttemplate

@@ -1595,6 +1595,7 @@ $endif
    * * [Fullscreen specification](http://www.w3.org/TR/fullscreen/) from W3C.
    */
   @SupportedBrowser(SupportedBrowser.CHROME)
+  @SupportedBrowser(SupportedBrowser.FIREFOX)
   @SupportedBrowser(SupportedBrowser.SAFARI)
   Future<void> requestFullscreen([Map? options]) {
     var retValue;