Fix emrun.test_no_browser to launch a browser using the BrowserCore harness (#26789)

Fix emrun.test_no_browser to launch a browser using the BrowserCore
harness, so that Firefox/Chrome/Safari will be launched with the
appropriate startup flags (and not e.g. try to autoupdate, or show modal
user prompts during the test run)

Author: juj

test/test_browser.py

@@ -5730,18 +5730,17 @@ def test_no_browser(self):
     proc = subprocess.Popen([EMRUN, '--no-browser', '.', '--port=3333'], stdout=PIPE)
     try:
       if get_browser():
-        print('Starting browser')
-        browser_cmd = shlex.split(get_browser())
-        browser = subprocess.Popen(browser_cmd + ['http://localhost:3333/hello_world.html'])
+        url = 'http://localhost:3333/hello_world.html?argv0'
+        print(f'Starting browser to {url}')
+        BrowserCore.browser_open(url)
         try:
           while True:
             stdout = proc.stdout.read()
             if b'Dumping out file' in stdout:
               break
         finally:
           print('Terminating browser')
-          browser.terminate()
-          browser.wait()
+          BrowserCore.browser_terminate()
     finally:
       print('Terminating emrun server')
       proc.terminate()