Bug 1791759 - Add support for content-visibility: auto r=emilio

This change adds support for `content-visibilty: auto` as well as
showing and hiding content based on the relevancy of the content as
defined in the specification. Changes to relevancy are handled by
triggering updates in a set of `content-visibility: auto` frames stored
in PresShell at the appropriate time in the document lifecycle.

Some tests are now failing due to this feature exposing the failures,
but they will be fixed in later changes.

This change is a reland of an earlier version that properly updates
intrinsic sizes and triggers an update of remembered size for the
purposes of contain-intrinsic-size when content relevancy changes.

Co-authored-by: Jihye Hong <jihye@igalia.com>

Differential Revision: https://phabricator.services.mozilla.com/D159693

dom/base/Selection.cpp

@@ -9,6 +9,8 @@
  */
 
 #include "mozilla/dom/Selection.h"
+
+#include "LayoutConstants.h"
 #include "mozilla/intl/BidiEmbeddingLevel.h"
 
 #include "mozilla/AccessibleCaretEventHub.h"
@@ -3200,6 +3202,7 @@ void Selection::NotifySelectionListeners() {
   PresShell* presShell = GetPresShell();
   if (presShell) {
     doc = presShell->GetDocument();
+    presShell->ScheduleContentRelevancyUpdate(ContentRelevancyReason::Selected);
   }
 
   // We've notified all selection listeners even when some of them are removed