Implement SSAOEffect

[vanruesc]

Description

Implement an SSAOEffect.

Related: #214, #245, #579

References:

• Postprocessing: Add SSILVB GI and AO mrdoob/three.js#29668
• https://github.com/GameTechDev/XeGTAO
• https://github.com/N8python/n8ao
• https://github.com/gkjohnson/threejs-sandbox/tree/master/gtaoPass
• Request: Support for dynamically scalable effect resolution #192 (comment)
• https://d29g4g2dyqv443.cloudfront.net/sites/default/files/akamai/gamedev%2Ffiles%2Fgdc12%2FGDC12_Bavoil_Stable_SSAO_In_BF3_With_STF.pdf
• https://github.com/asylum2010/Asylum_Tutorials/blob/master/Media/ShadersGL/gtaotemporaldenoiser.frag

Tasks

• Create SSAOEffect.
• Create ssao demo.
• Add unit test.

Implementation Details

• Find best SSAO technique before implementing (XeGTAO, SSRT3, GTVBAO, etc.).
• Should be done after TAAEffect and DenoisePass (bilateral blur) have been implemented.
• Consider adding support for light bounce. (should be handled by GI)