Fix for some post effects not scaling correctly when dynamic resolution is enabled on a camera's target texture

[christine-johnson]

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Purpose of this PR

Fixes https://fogbugz.unity3d.com/f/cases/1166603/ where some post effects were not scaling correctly when dynamic resolution is enabled on a camera's target texture. Dynamic resolution can be enabled on a camera (https://docs.unity3d.com/ScriptReference/Camera-allowDynamicResolution.html) or on a render texture (https://docs.unity3d.com/ScriptReference/RenderTexture-useDynamicScale.html), which means it can be enabled for a camera using Camera.allowDynamicResolution or Camera.targetTexture.useDynamicScale. We check both these cases internally but this isn't exposed in script, so we have to manually check both cases in ppv2.

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Testing status

Tested manually against https://fogbugz.unity3d.com/f/cases/1166603/ on Windows/DX12.
Ran yamato postprocessing tests

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Comments to reviewers

[ryanhy-unity]

Since post processing tests and manual verification done already I ran through some XR platforms not covered in the automated tests. Verified Oculus and Open XR runtimes both work fine and pass automated graphics tests. I was unable to verify Vulkan due to an existing issue however.