Since we don't want to expose video decoding API outside of GStreamer, the
header is removed from installation and both source files are renamed as
-private.
The header must remain in gst-libs because is referred by GstVulkanQueue,
which's the decoder factory.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6723>
The pool currently defaults to performing a layout transition to
VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL, with some special exceptions for
video usages. This may not be a legal transition depending on the usage.
Provide an API to explicitly control the initial image layout.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5881>