fix(pat-validation): Make sure to cancel submit events on invalid forms.

Make sure that submit events are canceled on invalid forms by using a
    capturing event handler which is invoked before non-capturing events.

The previous commit exposed a problem with the submit event handling,
    where the then non-capturing submit event handler was registered
    later than the one from pat-inject because pat-validation's async
    init method where pat-inject's init method is yet non-async. That
    happened even the pat-validation's pattern initialization is
    enforced to run first due to registration reordering in the Pattern
    registry. Now with the capturing event handler this problem is
    fixed.

Author: thet

src/pat/validation/validation.js

@@ -53,7 +53,11 @@ class Pattern extends BasePattern {
                     logger.debug("Checking input for submit", input, e);
                     this.check_input({ input: input, event: e });
                 }
-            }
+            },
+            // Make sure this event handler is run early, in the capturing
+            // phase in order to be able to cancel later non-capturing submit
+            // events.
+            { capture: true }
         );
 
         this.initialize_inputs();