A custom GtkLayoutManager is set to these objects, which calls into the
java handlers when measure or layout is requested.
Androids onMeasure method is quite different from GTKs measure method,
because Android already defines the final size during onMeasure.
Therefore, we call onMeasure from GTKs allocate callback instead of the
measure callback.
GtkWidgets extend GInitiallyUnowned and are automatically freed when
removing from parent widget. We need to add an extra reference, to make
sure the object keeps alive as long as the java widget has a reference
to it
Makes it easier to overwrite behavior in subclasses. Have a fallback
implementation for ViewGroup.
Save some _GET_LONG_FIELD / _SET_LONG_FIELD calls by directly passing
the native pointers to and from native methods.
NOTE: the main addition in this commit is WIP support for apps which
render on an EGL surface obtained using ANativeWindow_fromSurface
currently, this EGL surface is obtained by creating a 700x700 pixel
window with GLFW (the 700x700 size is hardcoded in several places)
and only Wayland is supported
ideally, we'd want to use a wayland subsurface to position the EGL
surface above the Surface widget it's associated with (and do
whatever for X11)
