This removes most macros from the function body decoder unittest. It
makes the {Validate} method (and the new {ExpectValidates} and
{ExpectFailure}) templates, to receive the code in different formats.

Drive-by: Rename "verify" to "validate".

R=titzer@chromium.org

Bug: v8:8562
Change-Id: I89e6125b52cf40a9539317bf16189208cd0592ab
Reviewed-on: https://chromium-review.googlesource.com/c/1458956Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59557}