Add source projection override for video outputs

This provides a way to specify whether the source projection should be used for the on-screen rendering, allowing VLC and libvlc application to enforce the rectangular view instead of the projected view, and allow to enforce a specific projection from the libvlc application.

The current goal is not to provide projection filtering (eg. changing from cubemap to equirectangular) but mostly to be able to enforce a rectangular projection rendering and avoid the mapping to 3D objects on the display, or generate equirectangular/cubemap (standard) sources and map them without embedding into a container to expose the metadata.

Implemented for d3d11 and opengl.