[Backport 2021.1][HDRP] Misc HDRP PRs (#3749)

* Fix a flickering issue related to moving shadow receivers (case 1302392) and a refactoring to avoid computing the same value for every effect. #3039

* The RTAO's history is now discarded if the occlusion caster was moving (case 1303418). #3343

* Update CHANGELOG.md

* Add new API to CachedShadowManager and fix WouldFitInAtlas #3387

* Added master stack documentation for HDRP (#3388)

* Added landing page and context/blocks overview page

* Added vertex context page and snippets

* Added the fragment context page and supporting snippets

* Added the decal master stack and the contexts intro

* Updated toc

* Added vertex context doc

* Update TableOfContents.md

* Added unlit doc

* Added lit master stack doc

* Added eye master stack doc

* Added fabric master stack

* added hair master stack

* Added stacklit master stack

* Added snippets to support shader stack work

* Fixed some formatting bugs

* Removed old links

* Updated links

* formatting

Co-authored-by: Lewis Jordan <[email protected]>
Co-authored-by: sebastienlagarde <[email protected]>

* Fix Sub-shadow rendering with cached shadows + Fix PCSS filtering issues on first frame or cached shadows #3396

* Reset ambient probe upon switching to very different skies bis #3423

* HDRP Graphic Test Fixes for Metal (#3408)

* Fixed the metal pipeline creation error message and updated several gfx test images.

* Rearranged LightData definition to workaround area lights not rendering issue on Intel GPUs on Catalina

* Updated 2501 reference image for Metal with the area light fix

* Updated 1550 and 2010 on Metal as previous were incorrect due to area light issue

Co-authored-by: Jeannette Yu <[email protected]>

* Custom Pass error message fix (#3424)

Typo in DrawRenderersCustomPass error message. Fixed a few other typos in this section too :D

* Add Unity version to what's new 11 (#3432)

* Update whats-new-11.md

* Updated the table of contents

* Shader abstraction cleanup #3443

* Some leftover caused by master merge (#3456)

* Fix multiple any hit occuring on transparent objects (case 1294927). #3471

* Colored Shadows update (#3486)

* Colored Shadows update

Included new information in the Color Shadow property description to tell the user that the Material's  Refraction Model has to be set to Thin, Box or Sphere for it to work.

* Fixed typo

Removed the "the" :D

* Revert "Fix multiple any hit occuring on transparent objects (case 1294927). #3471"

This reverts commit 0587177.

* Update 1219_Lit_Light_on_Tesselation.png

Co-authored-by: anisunity <[email protected]>
Co-authored-by: FrancescoC-unity <[email protected]>
Co-authored-by: Lewis Jordan <[email protected]>
Co-authored-by: Lewis Jordan <[email protected]>
Co-authored-by: Brandon Fogerty <[email protected]>
Co-authored-by: Jeannette Yu <[email protected]>
Co-authored-by: Vic Cooper <[email protected]>
Co-authored-by: robinb-u3d <[email protected]>

Author: 9 people

TestProjects/HDRP_Tests/Assets/GraphicTests/Scenes/2x_Lighting/2501_LightLayers/2505_LightLayers_RT.renderTexture

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