Add Sorting Layer Explorer for debugging of light batching

[kennytann]

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Purpose of this PR

Why is this PR needed, what hard problem is it solving/fixing?
https://jira.unity3d.com/browse/D2D-1667

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[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.
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Search for your PR branch using the sidebar on the left, 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
/.yamato%252Fall-urp.yml%2523PR_URP_2021.2

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