Bug 1824374 - implement popover activation behavior, r=emilio

See https://html.spec.whatwg.org/#the-input-element:popover-target-attribute-activation-behavior

Differential Revision: https://phabricator.services.mozilla.com/D175485

dom/html/HTMLInputElement.cpp

@@ -4083,7 +4083,10 @@ nsresult HTMLInputElement::PostHandleEvent(EventChainPostVisitor& aVisitor) {
           default:
             break;
         }  // switch
-      }    // click or outer activate event
+        if (IsButtonControl()) {
+          HandlePopoverTargetAction();
+        }
+      }  // click or outer activate event
     } else if ((aVisitor.mItemFlags & NS_IN_SUBMIT_CLICK) &&
                (oldType == FormControlType::InputSubmit ||
                 oldType == FormControlType::InputImage)) {