This is needed to allow 2D to fully make use of 3D effects (e.g. glow), and can be used to substantially improve quality of 2D rendering at the cost of performance
Additionally, the 2D rendering pipeline is done in linear space (we skip linear_to_srgb conversion in 3D tonemapping) so the entire Viewport can be kept linear.
This is necessary for proper HDR screen support in the future.
This allows light sources to be specified in physical light units in addition to the regular energy multiplier. In order to avoid loss of precision at high values, brightness values are premultiplied by an exposure normalization value.
In support of Physical Light Units this PR also renames CameraEffects to CameraAttributes.
