GC allocations during Entities extraction

Steps to reproduce:

1. See https://discussions.unity.com/t/surface-cache-gi-preview/1720494/404

Actual results: There are GC allocations during extraction

Expected results: There should be no GC allocations during extraction

Reproducible with versions: 7000.0x, 6000.7x

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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