Handle IPC descriptor serialization

[grovesNL]

Follow-up from #20:

• How do we need to handle serialization/deserialization for descriptors when using IPC?
• Which parts need to be handled within wgpu-native vs. the caller?
• Should we change the types of descriptors to const uint8_t *desc (i.e. binary serialized) for the remote case in wgpu.h? (already done)

[kvark]

Related to #146 (comment)