Blender Git Loki

Draw Manager: Implement render info for external engines

This can be used by any engine actually. For example to give feedback
regarding probe caching in Eevee, ....

Unline master, we try to conciliate both the original viewport info
(FPS, view name) and the render info.

Note: I had to split the function in two because the camera alpha
passepartout is handled inside the view3d_draw_region_info function.

Review: Campbell Barton and Clement Foucault.

Thanks to Sergey Sharybin and Pablo Vazquez for some of the design
discussions.