Implement SSREffect

[vanruesc]

Description

Implement an SSREffect.

Related: #190, #348

References:

• https://threejs.org/examples/?q=ssr#webgl_postprocessing_ssr
• https://github.com/Domenicobrz/WebGL2-Screen-space-reflections
• https://lettier.github.io/3d-game-shaders-for-beginners/screen-space-reflection.html
• https://github.com/gkjohnson/threejs-sandbox/tree/master/screenSpaceReflectionsPass
• https://github.com/0beqz/realism-effects

Tasks

• Create SSREffect.
• Create ssr demo.
• Add unit test.

Implementation Details

• Use G-Buffer components (depth, normals, ORM).
• Calculate world position based on depth.
  • Use <pp_depth_utils_pars_fragment> shader chunk.