Add fillignore attribute to transclude widget to fix visible transclusion (#7451)

* slotignore attribute for transclude widget to fix visible transclusion

Fixes #7449

* Remove unneeded depth attribute

No longer needed

* Replace "slotignore" by "fillignore"

core/modules/widgets/transclude.js

@@ -384,6 +384,13 @@ TranscludeWidget.prototype.getTransclusionSlotFill = function(name,defaultParseT
 	}
 };
 
+/*
+Return whether this transclusion should be visible to the slot widget
+*/
+TranscludeWidget.prototype.hasVisibleSlots = function() {
+	return this.getAttribute("$fillignore","no") === "no";
+}
+
 /*
 Compose a string comprising the title, field and/or index to identify this transclusion for recursion detection
 */