Since the texture release mechanism is same for both gtk-egl
and gtk-glarea, move the helper from gtk-egl to common gtk
code so that it can be shared by both gtk backends.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Message-Id: <20210914211837.3229977-2-vivek.kasireddy@intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>