Add the vulkan video decoder to the compositor

[jerzywilczek]

closes #751.

The decoder structure:

1. data comes into the parser, which turns it into decoder instructions
   • first it aggregates the NAL units into Access Units (basically whole frames)
   • then the hardest part happens: reference management. for each frame that needs to be decoded, a list of necessary reference pictures is generated based on quite complicated conditions
2. the instructions are fed into the decoder, which executes them, basically decoding the frames
   • the decoder does two things. the first one is managing the state of the structures necessary for decoding. This mostly happens on processing SPS packets.
   • the other thing is just translating the instructions into vulkan structs, which can be fed to the GPU

[wkozyra95]

Can you add an example of initiating graphics context directly in a way where users have access to e.g. adapter

[jerzywilczek]

sure

[jerzywilczek]

just realized that I need a mac os computer to write the mac os part of the example. I'll have access to a mac next week. Do you think we can marge the example as-is?

[noituri]

The parts I understood looked good to me ✅