Auto merge of #22224 - pyfisch:composition-webdriver, r=nox

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.

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components/script/dom/htmltextareaelement.rs

@@ -13,6 +13,7 @@ use crate::dom::bindings::error::ErrorResult;
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::root::{DomRoot, LayoutDom, MutNullableDom};
 use crate::dom::bindings::str::DOMString;
+use crate::dom::compositionevent::CompositionEvent;
 use crate::dom::document::Document;
 use crate::dom::element::RawLayoutElementHelpers;
 use crate::dom::element::{AttributeMutation, Element};
@@ -576,6 +577,22 @@ impl VirtualMethods for HTMLTextAreaElement {
                         &window,
                     );
             }
+        } else if event.type_() == atom!("compositionstart") ||
+            event.type_() == atom!("compositionupdate") ||
+            event.type_() == atom!("compositionend")
+        {
+            // TODO: Update DOM on start and continue
+            // and generally do proper CompositionEvent handling.
+            if let Some(compositionevent) = event.downcast::<CompositionEvent>() {
+                if event.type_() == atom!("compositionend") {
+                    let _ = self
+                        .textinput
+                        .borrow_mut()
+                        .handle_compositionend(compositionevent);
+                    self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
+                }
+                event.mark_as_handled();
+            }
         }
     }