[dev.simd] cmd/compile: add INSERT[IF]128 instructions

[dev.simd] cmd/compile: add INSERT[IF]128 instructions

This CL is created by simdgen CL 684055 and
should be submitted after it.

Also includes a test.

Change-Id: I2ad7ae51d11cfc19745e866150e2eaf010d4ea49
Reviewed-on: https://go-review.googlesource.com/c/go/+/684077
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>