Switch ww_applet_support.js from using a submit handler to click handlers on the submit buttons.

This makes applet problems work in the PG problem editor of webwork2.
The PG problem editor uses click handlers on the submit buttons as well,
but calls `preventDefault` on the event, and prevents the form
submission from occuring.  That prevents the current submit handler set
in the ww_applet_support.js code from happening.  Thus the answers for
applets do not get submitted.  By using the click handlers this gets in
at the same point that the PG problem editor handlers are, and they
still occur.  All click handlers are executed even if one of them
prevents default behavior.

Author: drgrice1

htdocs/js/AppletSupport/ww_applet_support.js

@@ -274,12 +274,14 @@ class ww_applet {
 		if (form.submitHandlerInitialized) return;
 		form.submitHandlerInitialized = true;
 
-		// Connect the submit action handler to the form.
-		form.addEventListener('submit', () => {
-			for (const appletName in ww_applet_list) {
-				ww_applet_list[appletName].submitAction();
-			}
-		});
+		// Connect the submit action handler to the form submit buttons.
+		for (const button of form.querySelectorAll('input[type="submit"]')) {
+			button.addEventListener('click', () => {
+				for (const appletName in ww_applet_list) {
+					ww_applet_list[appletName].submitAction();
+				}
+			});
+		}
 	};
 
 	// Initialize applet support and the applets.