Allow hooking into image barriers / texture transitions on a backend-specific basis

[JMS55]

Is your feature request related to a problem? Please describe.
I'm trying to hook into FidelityFX Super Resolution 2, a Vulkan/DirectX12 library. This library handles all the dispatches, but requires that the input textures have a certain VkAccessFlagBits, and be in a certain VkImageLayout (or the DX12 equivalents, for DX12).

Describe the solution you'd like
Add a command encoder transition_textures() method that hooks into wgpu's resource tracker, and adds a transition to the next pipeline image barrier (if necessary) to a specific user provided VkImageLayout for Vulkan, or similar thing for DX12 and others.

Describe alternatives you've considered
I've tried doing such a thing here. I ran into the problem that wgpu_hal::TextureUses is too high level - I can't specify or coerce it to get a specific VkImageLayout. I'm also unsure if it would work correctly or if I made other mistakes.

[cwfitzgerald]

This is obsoleted by #4067