Urp/depth priming tests

[NicoLeyman]

Purpose of this PR

The recently landed PR adding Depth Priming didn't contain any automated test coverage. This PR aims to correct that by adding a new graphics test.
Since this test ran into an issue related to the recent swapbuffer changes this also contains a fix for that to allow the test to succeed.

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Testing status

New graphics test added. Ref images are being added.

The test shows a set of boxes rendered with a camera stack, splitscreen rendering. Since Depth Priming can have fallout I opted to use some of the existing materials on the scene objects. SSAO and transparent materials are included and definitely need to stay part of the test.

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Comments to reviewers

Code changes provided by Robin.

[github-actions]

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[phi-lira]

Note for RM: this class is internal, not breaking change to user.

[simon-engelbrecht-soerensen]

Would be nice to have screenshots of ref images that were added in the PR.
Otherwise looks good.

[robin-demoor]

LGTM

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://unity-ci.cds.internal.unity3d.com/project/902/
Search for your PR branch using the search bar at the top, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

URP
/jobDefinition/.yamato%252Fall-urp.yml%2523PR_URP_trunk
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[phi-lira]

This PR introduced the following error in ABV:
severity: Error
message: '' is an incorrect path for a scene file. BuildPlayer expects paths relative to the project folder.

[cdxntchou]

I think you can revert the ShaderGraph test reference images, they have been added to master already.