Modeled after Metal's cb.GPUStart/EndTime. Implemented with timestamp
queries for other APIs.
Implemented for Metal, D3D11, Vulkan for now. No more callback, just
a getter on the command buffer which returns the latest known value,
referring to some previous frame. This makes it a lot more usable
than the original solution that is not really used anywhere at
the moment.
Now works for offscreen "frames" as well, this was not implemented
before.
Opt in with a new QRhi::create() flag because we cannot tell in
advance if the getter will be called or not, and this way we can
skip recording the timestamps by default. The cost is probably
minimal, though. Qt Quick will set this automatically when running
with QSG_RHI_PROFILE=1.
Change-Id: I903779984a4e0bbf1d03806d04bf61571ce23d72
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
e539e9a7af