Has wider support than gather / scatter, and is faster.

Bug: b/135609394
Change-Id: Ib1435331f3130fbef7cbf9eaf1c0c2570a0ec2a1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33169Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>