Implement f32x4.splat and enable handling this in Liftoff.

We add a new macro for defining test cases to run on TurboFan, Liftoff,
interpreter, and scalar lowering.

Also add an assertion that the execution tier used is what we expected
it to be. This is useful for Liftoff, because by default it falls back
to TurboFan when it encounters an unimplemented opcode.

Bug: v8:9909
Change-Id: I594955fce778173191fc44c38c4f956a05e77839
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2014753
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65954}