SpirvShader had a lot of utility functions in an anonymous namespace
at the top of the file. Given that we're going to try splitting up this
huge file, we need somewhere common for this code to live.
ShaderCore looks like the most appropriate place for this right now.

Bug: b/145336353
Change-Id: If4137875098fbeb761fdf63caf8d45011236cff1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38809
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Ben Clayton <bclayton@google.com>