LibWeb/UIEvents: Implement TextEvent

Author: https://github.com/jamierocks
Commit: f610a12671
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/701
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/tcl3

Userland/Libraries/LibWeb/Forward.h

@@ -731,6 +731,7 @@ class InputEvent;
 class KeyboardEvent;
 class MouseEvent;
 class PointerEvent;
+class TextEvent;
 class UIEvent;
 }