As a companion to go with the platform_change api,
add a gtk_accessible_get_platform_state() function
that can be used by backends to get the platform
state.
This is in preparation for making entries inherit
their focus states from the text widget within.
Similar to gtk_widget_should_layout(), add a
gtk_accessible_should_present() function that backends can
use to determine whether an accessible should be presented
or not.
Ways to make a widget not presented in a11y:
- hide the widget
- set its role to NONE
- make it have a NULL AT context
We will use this in future to hide the GtkText inside
an entry, since the Text implementation will be done
by the wrapper.
Add an enum for 'platform changes' to the at context
change notification mechanism. This will let us pass
along things that ARIA considers 'platform state' such
as focus or editability. The difference between the
platform state and other ARIA states is that we don't
keep the platform state separately in the at context
- backends are expected to just query the widgets.
This is just about avoiding notify listeners for
change notification.
An Accessible implementation must create an ATContext object. UI
elements are supposed to interact with the GtkAccessible API, but we
expose GtkATContext to allow patterns like delegation.
