* add ability to specify on MeshDepthMaterial the type of depth packing one wants.

* depthRGBA -> clipZRGBA - more correct name.

* forgotten replace of depthRGBA -> clipZRGBA.

* add MeshDepthMaterial depthFormat + depthPacking.  Use equations compatible with z buffers.

* adopting MeshDepthMaterial instead of clipZRGBA.

* remove clipZRGBA shader (aka depthRGBA shader) as we can now use MeshDepthMaterial for it.

* remove some comments.

* enable skinning in MeshDepthMaterial, as it was enabled in depthRGBA material.

* remove unused shader.

* fix bug.

* fix bug in shadows with MEshDepthMaterial.

* remove unnecessary debug code.

* ensure that skinning and morphTargets propagate with MeshDepthMaterial.

* fix ssao example to use new MeshDepthMaterial.

* remove unused code.

* Implemented user-defined clipping planes.

* Renderer: Minor documentation update.

* Implements object-level clipping.

* Renderer: Minor cosmetic changes.

* Fixed lethal typo in normal shader.

* Let shadows respect .side of object's material.

* Fixed Plane.applyMatrix4.

- Scale denormalized but did not scale the position
- Projection is not supported (solved by documentation)
- Removed unnecessary copying to make up for the normalization
- Still arguably too heavy

* Added custom clipping example.

* Clipping: Fixed transition to disabled state.

* Improved custom clipping example.

- GUI dependency of volume visualization on Enabled state
- Larger radius for cylindrical global clipping area

* No .matrixAutoUpdate = false in clipping example.

* Let ShadowMap check renderer.localClippingEnabled.

* Added a simplified clipping example.

* Reintroduce MeshPhysicalMaterial

* Reintroduce MeshPhysicalMaterial

* Simplified conditionals

float and half HDR CUbe Maps load and are properly generated.  Something wrong when using RGBE encoding.

clean up per @mrdoob's comment here: https://github.com/mrdoob/three.js/pull/8217#discussion_r54030483