Reland Input type=text Shadow DOM With Performance Improvement (#37483)

Depends on #37427.

In addition to the changes introduced by
https://github.com/servo/servo/pull/37065, there are several performance
improvements and nits as follows:
- Use the internal pseudo element for style matching, this will reduce
the performance regression by ~66%.
- Manual construction of the `Text` node inside a text container. This
is followed by the modification of the inner `Text` node instead of
using `SetTextContent` which is more expensive.
- Use `implemented_pseudo_element` instead of
`text_control_inner_editor` `NodeFlag` to handle the special cases that
these elements should follow, specifically the:
  - focus delegation workaround;
  - selections; and
  - line height resolving.
- More documentation.

Servo's side of: https://github.com/servo/stylo/pull/217

Testing: No new unexpected WPT failure, except for the one introduced by
https://github.com/servo/servo/pull/37065/.
Fixes: #36307 #37205

---------

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

components/script/dom/document.rs

@@ -1556,11 +1556,14 @@ impl Document {
                 return;
             }
 
+            // For a node within a text input UA shadow DOM, delegate the focus target into its shadow host.
+            // TODO: This focus delegation should be done with shadow DOM delegateFocus attribute.
+            let target_el = el.find_focusable_shadow_host_if_necessary();
+
             self.begin_focus_transaction();
-            // Try to focus `el`. If it's not focusable, focus the document
-            // instead.
+            // Try to focus `el`. If it's not focusable, focus the document instead.
             self.request_focus(None, FocusInitiator::Local, can_gc);
-            self.request_focus(Some(&*el), FocusInitiator::Local, can_gc);
+            self.request_focus(target_el.as_deref(), FocusInitiator::Local, can_gc);
         }
 
         let dom_event = DomRoot::upcast::<Event>(MouseEvent::for_platform_mouse_event(