vulkan/context: always initialize all queues

To improve compatibility with other users of this VkDevice (notably FFmpeg), we need to create e.g. decoding/encoding queues, when available.

In practice, these shouldn't show up unless the necessary extensions are enabled, so this is a no-op in most circumstances. At worst, we waste a tiny bit of driver memory and overhead.

To preserve API compatibility, we still only announce the basic queues in pl_vulkan.queues. Deprecate the field on account of this limitation.