Implement DepthOfFieldEffect #569

Description

Implement a DepthOfFieldEffect based on the implementation in v6.

References:

• https://www.adriancourreges.com/blog/2018/12/02/ue4-optimized-post-effects/

Tasks

• Create CoC shader.
• Create blur shader.
• Create DepthOfFieldEffect.
• Create depth-of-field demo.
• Add unit test.

Implementation Details

• Check the linked article for potential improvements.
• Should be done after PoissonBlurMaterial has been implemented.
• The CoC should be calculated based on fragment distance instead of depth.
• Add support for logarithmic depth.
• Consider adding options for fringe/chromatic aberration and luminance gain.