Emit crossing events - with a new GTK_CROSSING_DROP type - like we do
for motion events. There is no more special casing for them.
Note that the gesture has not been updated yet, so some obscure behavior
may occur.
We don't want to expose the GtkCrossingData struct, and manually
feeding events to event controllers is not something we want to
encourage, going forward.
Instead of relying on gdk's antiquated crossing events,
create a new GtkCrossingData struct that contains the
actual widgets, and a new event controller vfunc that
expects this struct. This also saves us from making sense
of X's crossing modes and details, and makes for a
generally simpler api.
The ::focus-in and ::focus-out signals of GtkEventControllerKey
have been replaced by a single ::focus-change signal that
takes GtkCrossingData as an argument. All callers have
been updated.
We want to make events readonly, so stop translating
their coordinates and instead pass the translated
coordinates separately, when propagating events.
This is the first step towards refactoring how widgets deal with event
controllers.
In the future, the widget will treat controllers the same way it treats
child widgets:
1. The controllers will be created without a widget.
2. There will be gtk_widget_add/remove_controller() functions to add
or remove controllers.
3. The widget will hold a reference to all its controllers.
This way we will ultimately be able to automate controllers with ui
files.
This will be used right before handle_event() in order to filter
out events, useful to make the previous "no touchpad events" behavior
the default, and have gesture subclasses include manually the touchpad
events they handle.
