Imported changes from Oculus-VR:Unity-Graphics:6000.0/17.0.4-subpass

[Torgo13]

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Checklist for PR maker

• Have you added a backport label (if needed)? For example, the need-backport-* label. After you backport the PR, the label changes to backported-*.
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Purpose of this PR

The Oculus-VR fork has branches with Vulkan subpass support for Unity 2022.3 and Unity 6000.0. This branch applies the same changes to Unity 6000.3.

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Testing status

The following test projects from the Oculus-VR 17.0.4-subpass branch work correctly in Unity 6000.3.12f1. They display the correct output and demonstrate subpass merging on both Windows and Android devices using the Vulkan API.
DepthInputSubpassSample
PostProcessSubpassSample

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Comments to reviewers

Ideally this branch would include the original commits to the Oculus-VR branch to maintain the Git history and credit the original developers. This is a proof-of-concept demonstration that these same changes can be used in a later LTS version of Unity.