Dynamic stencil reference

[msiglreith]

Setting stencil reference per command requires marking it as dynamic state in the graphics pipeline which at least the vulkan backend doesn't do atm

[kvark]

So this needs to be addressed in gfx-rs first, was missing from gfx-rs/gfx#1567 ?

[msiglreith]

@kvark yes, it appears what's supported so far for the vulkan backend and hal is:
Viewport, Scissor, Blend Constants and Depth Bounds

Comparing with vkspecs what would be missing from core so far is: line width, depth bias, stencil compare mask, stencil write mask and stencil ref

[kvark]

btw, depth bias is there
Created gfx-rs/gfx#2905 for the rest

[kvark]

This is fixed by #282