video resolutions

@smalis-msft @jstarks

at the moment only 1024x768 and 1280x1024 is supported.
without touching the vram we can support 640x480 ... 1920x1080,
when touching the vram we can go up to 2560x1600

i can do that - do You want :

a) not touching the vram, just add resolutions
b) touching vram also, bump up until 2560x1600
c) make a parameter how much vram we want to allocate, and make offered resolutions dependent on that ?
d) make a parameter with the max resolution, and allocate vram dependent on that ? (my preference)

if we change vram, I guess your screenshot tests will also need to be adopted.

at the curren ram prices ;-) it would be kind of cool if we´d only allocate the vram needed, not the fixed 8MB. I just hit that looking for further VNC optimisations.

just steer me, I will do the footwork

First confirm which of the four resolution and VRAM-allocation options is wanted, since the issue does not select an implementation. Then locate the existing resolution and fixed 8MB VRAM handling in OpenVMM, review the screenshot tests mentioned in the issue, and update them so the supported resolutions and allocation behavior are covered.