[HDRP Backport 21.2] Backport various PRs

[sebastienlagarde]

Purpose of this PR

• Fixed initial decal position Fixed initial decal position #5889
• Fix APV issue spewing asserts when baking with max subdiv level of 2 (Fix APV issue spewing asserts when baking with max subdiv level of 2 #5888)
• Skip refresh ops if feature is disabled. (Fix issue with refresh on APV baking window when APV is disabled #5886)
• Fixed the clouds not taking properly into account the fog when in distant mode and with a close far plane (case 1367993). (Fixed the clouds not taking properly into account the fog when in distant mode and with a close far plane (case 1367993). #5884)
• To info box (Change warning about APV being off in the HDRP asset to an info box #5879)
• Add override checkbox. (Add override checkbox for probe volumes subdiv level overrides  #5878)
• corrected links to HDAdditionalLightData and HDLightTypeAndShape (corrected links to HDAdditionalLightData and HDLightTypeAndShape #5861)
• updated link to expert guide (updated link to expert guide #5857)
• Add comment (Add comment around double string constant for prev exposure #5853)
• [HDRP][Path Tracing] Added selection of light types for Unlit shadow mattes. [HDRP][Path Tracing] Added selection of light types for Unlit shadow mattes. #5855
• Maintain APV cells loaded if at least one scene still references that cell (Maintain APV cells loaded if at least one scene still references that cell  #5900)
• Add a basic APV test to runtime tests (Add a basic APV test to runtime tests #5952)
• [HDRP] APV - Fix voxelization issues with planes at the origin ([HDRP] APV - Fix voxelization issues with planes at the origin #5897)
• Fix another issue with probe volume subdiv multiplier when changing to a lower subdiv level (Fix another issue with probe volume subdiv multiplier when changing to a lower subdiv level #5893)
• Fixed the volumetric clouds debug view not taking into account the exposure and leading to Nans (case 1365054). (Fixed the volumetric clouds debug view not taking into account the exposure and leading to Nans (case 1365054). #5940)
• Change order of fields in the cbuffer. ([HDRP] Fix APV issue on Vulkan, PS4 - Change order of fields in the cbuffer. #5980)
• Fixed the dependency between transparent SSR and transparent depth prepass being implicit (case 1365915). (Fixed the dependency between transparent SSR and transparent depth prepass being implicit (case 1365915). #5898)
• Updating docs for merged PRs (Updating docs for merged PRs #5821)
• [Fogbugz # 1365687] Fixing depth pyramid with multicamera on hardware drs. [Fogbugz # 1365687] Fixing depth pyramid with multicamera on hardware drs. #5902
• Fix (Fix APV contribution in volumetric fog #5994)
• release cmd (Release cmd buffer used when during probe volume subdiv #5993)
• test linux vulkan and OSX filter out. (Re-enable APV test on Linux Vulkan, but disable on OSX.  #5989)
• Fixed removal of depth buffer binding (Fixed removal of depth buffer binding #5910)
• [HDRP][Path Tracing] Added orthographic camera support [HDRP][Path Tracing] Added orthographic camera support #5944
• Fixed a regression in the transparent SSR color pyramid usage. (Fixed a regression in the transparent SSR color pyramid usage. #6001)
• [HDRP] Reenable crossfade on the HD SpeedTree 8 shader. [HDRP] Reenable crossfade on the HD SpeedTree 8 shader. #5957
• Force scalarization of shadow index data off (Fix issues with shadows and volumetric fog on PS5 (potentially PS4 too) #6007)
• Fixes for light anchor Fixes for light anchor #5915
• Minor performance improvements to SSGI (case 1367144). Minor performance improvements to SSGI (case 1367144). #5921

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HDRP
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