[Backport 2021.1][HDRP] Multiple HDRP PR backport (#3731)

* Fix issue with register spilling in light list shaders #3016

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

* Merge Hd/bugfix #3047

* [HDRP]Improvements and fixes on Volumes Components Inspectors #3072

* Fix XR depth copy and MSAA #3075

* [HDRP][Compositor] Fix issues with compositor's undo #3100

* Hdrp/docs/fix 1305538 (#3112)

* Added information about using recursive rendering and other effects

* Fixed formatting

* [HDRP] Merge Hd/bugfix #3120

* Formatting

Co-authored-by: FrancescoC-unity <[email protected]>
Co-authored-by: anisunity <[email protected]>
Co-authored-by: alex-vazquez <[email protected]>
Co-authored-by: Fabien Houlmann <[email protected]>
Co-authored-by: Pavlos Mavridis <[email protected]>
Co-authored-by: Lewis Jordan <[email protected]>

Author: 7 people