* Add 'frameNumber' to Frame struct
Previously, the frame number returned from bgfx::frame() was tracked separately in the Context. Now,
we store that information in the Frame. This will allow us to attach the frame number to ViewStats.
* Add frame number to ViewStats
When ViewStats are enabled, we tag each timer query with the current frame number, then include
that information in the final results. In this way, clients can correlate specific work that they
submitted to specific GPU timing information.
NOTE: Some backends not implemented, yet. They will always have 0 for frame number.
The ones which are implemented are:
* OpenGL
* Vulkan
* D3D 9,11,12
* Noop
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