vulkan: implement caching and reuse of a couple of vulkan resources

vulkan: implement caching and reuse of a couple of vulkan resources

Includes a new GstVulkanHandlePool base class for pooling different
resources togther.  The descriptor cache object is ported to
GstVulkanHandlePool with the exact same functionality.

A new GstVulkanFenceCache is also implemented for caching fences
which is used internally by GstVulkanDevice for creating or reusing
fences.

The existing GstVulkanTrashFenceList object now caches trash objects.