Extensions and layers can be enabled before calling
gst_vulkan_instance_open() but after calling
gst_vulkan_instance_fill_info().
Use the list of available extensions to better choose a default display
implementation to use based on the available Vulkan extensions for surface
output.
Defaults are still the same.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1341>