This implements most of the CloseWatcher API from the html spec.
AbortSignal support is unimplemented.
Integration with dialogs and popovers is also unimplemented.
(cherry picked from commit b216046234560df531e1a32269e5dfa18f8f240c, manually amended to replace a single UIEvents::KeyCode::Key_Escape with KeyCode::Key_Escape in EventHandler.cpp since we don't have the second commit of https://github.com/LadybirdBrowser/ladybird/pull/86)
This implements most of the CloseWatcher API from the html spec.
AbortSignal support is unimplemented.
Integration with dialogs and popovers is also unimplemented.
(cherry picked from commit b216046234560df531e1a32269e5dfa18f8f240c, manually amended to replace a single
UIEvents::KeyCode::Key_EscapewithKeyCode::Key_Escapein EventHandler.cpp since we don't have the second commit of https://github.com/LadybirdBrowser/ladybird/pull/86)Cherry-picks https://github.com/LadybirdBrowser/ladybird/pull/240/