try-login: use requestSubmit for form submissions

`form.submit()` performs a low-level form submission that bypasses HTML
validation, submit events, and submitter handling.

`requestSubmit()` triggers the full browser submission flow, matching the
behavior of a real user clicking the submit button, including form validation.

https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/requestSubmit

Author: netoarmando

brozzler/js-templates/try-login.js.j2

@@ -42,7 +42,7 @@ var __brzl_tryLogin = function() {
             console.log('submitting username=' + usernameField.value
                         + ' password=*** to detected login form');
             try {
-                form.submit();
+                form.requestSubmit();
             } catch (e) {
                 // "If a form control (such as a submit button) has a name or
                 // id of 'submit' it will mask the form's submit method." -MDN

tests/test_brozzling.py

@@ -297,7 +297,7 @@ def on_response(msg):
     login_url = "http://localhost:%s/login-action" % httpd.server_port
     # When username and password are defined and initial page has login form,
     # detect login form, submit login, and then return to the initial page.
-    username = "user1"
+    username = "user1@example.com"  # input type="email"
     password = "pass1"
     with brozzler.Browser(chrome_exe=chrome_exe) as browser:
         browser.browse_page(