A bunch of small fixes and Vulkan features

[GaelCathelin]

Hello! First of all thank you so much for this wonderful abstraction, it makes my life so much easier.

I've been using it as the main building block of a Vulkan abstraction (I don't use the DX backends at all) for more than a year and I wanted to share some fixes and small features that I did on the Vulkan backend: https://github.com/GaelCathelin/nvrhi/commits/main?author=GaelCathelin

If you're interested, let me know if you want one or several pull requests.

On the experimental branch there are more commits (the 4 on the top the list) that are likely incompatible with the other backends but they fixed some roadblocks that I had while implementing automatic BindingSets generation with shader reflections on top of NVRHI, and I'm not 100% confident that I did the right thing.

[apanteleev]

Thank you for the offer!

If you could submit your changes as multiple PRs (one per feature, or maybe grouping some closely related features together), that would be great. But before that, please minimize the diffs by reverting any whitespace-only changes, and make the new features work on all graphics APIs where possible/applicable.