Shader Compilation for projects with lots of Shaders can be slow (i.e. VFX Graph asset heavy projects)

Steps to reproduce:

1. Have a project with lots and lots of individual shaders.  A production example of a project with 1000 VFX Assets resulted in over 15k individual shaders.  Shader compilation during build takes > 1hour on i9-10980xe

2. Build the project, watch CPU utilisation during shader compilation stage.

Actual results: Shader compilation time during build can be incredibly slow as the shaders are compiling linearly on a single-thread.  The number of shader-variants (post-stripping) should be very low so this scenario is not taking advantage of shader-variant multi-threading.

Expected results: Individual shaders are compiled over multiple threads to take advantage of multi-threading.

Reproducible with versions: All

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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