This will allow us to reuse this code across unit tests and benchmarks.

Bug: b/176981107
Change-Id: Ie5ea3708cb959dbd0189658b42f01bad998ae94a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51869Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>