[IMP] app: rethrow errors that were not handled

This commit makes it so that when an error occurs in an owl app and none
of the registered error handlers are able to handle it, we rethrow the
error instead of just logging it to the console and swallowing it. This
allows users of owl to handle errors that happen in owl applications by
using event listeners for error and unhandledrejection events on the
window.

tests/helpers.ts

@@ -261,6 +261,20 @@ expect.extend({
   },
 });
 
+export function nextAppError(app: any) {
+  const { handleError } = app;
+  return new Promise((resolve) => {
+    app.handleError = (...args: Parameters<typeof handleError>) => {
+      try {
+        handleError.call(app, ...args);
+      } catch (e: any) {
+        app.handleError = handleError;
+        resolve(e);
+      }
+    };
+  });
+}
+
 declare global {
   namespace jest {
     interface Matchers<R> {