webdriver: Implement maximize window for both headless&headed window (#38271)

- Implement [Maximize
Window](https://w3c.github.io/webdriver/#maximize-window)
- Previously, headless window screen size is same as inner size if not
specified in preference. We make it double as required by the test to
not have max window initially.
- Some other random cleanup.

Testing: webdriver Stress test for maximize window (headed + headless).

---------

Signed-off-by: Euclid Ye <euclid.ye@huawei.com>

ports/servoshell/desktop/headed_window.rs

@@ -767,10 +767,7 @@ impl WindowPortsMethods for Window {
         // this prevents a crash in the compositor due to invalid surface size
         self.winit_window.set_min_inner_size(Some(PhysicalSize::new(
             MIN_INNER_WIDTH,
-            i32::max(
-                MIN_INNER_HEIGHT,
-                (self.toolbar_height() * self.hidpi_scale_factor()).0 as i32,
-            ),
+            MIN_INNER_HEIGHT.max((self.toolbar_height() * self.hidpi_scale_factor()).0 as i32),
         )));
     }
 
@@ -808,6 +805,10 @@ impl WindowPortsMethods for Window {
             Some(winit::window::Theme::Light) | None => servo::Theme::Light,
         }
     }
+
+    fn maximize(&self, _webview: &WebView) {
+        self.winit_window.set_maximized(true);
+    }
 }
 
 fn winit_phase_to_touch_event_type(phase: TouchPhase) -> TouchEventType {