While having the base units as sizeof(float) is handy (as that's the smallest unit we currently support), it makes limit checking tricky as we're continually converting units of byte <-> float.

This sets us up nicely for when we want to support smaller types.

Change-Id: I3e334b6df4899f433b281118be23fdf8df6d9829
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29328
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>