This namespace declares typedefs that represent per-lane-scalars.

Once we start mixing per-lane storage with linear external memory, this will help readability.

Bug: b/126126820
Change-Id: Ia128c3cc97dd77b3d5c4b7bd9537c19427a9ac3f
Reviewed-on: https://swiftshader-review.googlesource.com/c/25548
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Ben Clayton <bclayton@google.com>