[py] Improve how desired_capabilities and options are merged

The code  has been moved around over time so have take the gist of
the original PR by @earendil and made it work. Original PR in #7348

Author: AutomatedTester

py/selenium/webdriver/chrome/webdriver.py

@@ -65,6 +65,3 @@ def __init__(self, executable_path="chromedriver", port=DEFAULT_PORT,
                                         port, options,
                                         service_args, desired_capabilities,
                                         service_log_path, service, keep_alive)
-
-    def create_options(self) -> Options:
-        return Options()

py/selenium/webdriver/chromium/webdriver.py

@@ -64,16 +64,14 @@ def __init__(self, browser_name, vendor_prefix,
 
         _ignore_proxy = None
         if not options:
-            # desired_capabilities stays as passed in
-            if not desired_capabilities:
-                desired_capabilities = self.create_options().to_capabilities()
-        else:
-            if not desired_capabilities:
-                desired_capabilities = options.to_capabilities()
-            else:
-                desired_capabilities.update(options.to_capabilities())
-            if options._ignore_local_proxy:
-                _ignore_proxy = options._ignore_local_proxy
+            options = self.create_options()
+
+        if desired_capabilities:
+            for key, value in desired_capabilities.items():
+                options.set_capability(key, value)
+
+        if options._ignore_local_proxy:
+            _ignore_proxy = options._ignore_local_proxy
 
         self.vendor_prefix = vendor_prefix
 
@@ -204,5 +202,5 @@ def quit(self) -> NoReturn:
         finally:
             self.service.stop()
 
-    def create_options(self):
-        pass
+    def create_options(self) -> Options:
+        return Options()