Forward WebDriver CompositionEvent

Dispatch composition events in JS.
Insert characters from composition events to text input.

CompositionEvents currently can only be
created by WebDriver and not by embedders.

components/script/textinput.rs

@@ -6,6 +6,7 @@
 
 use crate::clipboard_provider::ClipboardProvider;
 use crate::dom::bindings::str::DOMString;
+use crate::dom::compositionevent::CompositionEvent;
 use crate::dom::keyboardevent::KeyboardEvent;
 use keyboard_types::{Key, KeyState, Modifiers, ShortcutMatcher};
 use std::borrow::ToOwned;
@@ -831,6 +832,11 @@ impl<T: ClipboardProvider> TextInput<T> {
             .unwrap()
     }
 
+    pub fn handle_compositionend(&mut self, event: &CompositionEvent) -> KeyReaction {
+        self.insert_string(event.data());
+        KeyReaction::DispatchInput
+    }
+
     /// Whether the content is empty.
     pub fn is_empty(&self) -> bool {
         self.lines.len() <= 1 && self.lines.get(0).map_or(true, |line| line.is_empty())