Instead of creating temporary {std::vector}s (which always allocate on
the heap) create more vectors on the stack, via initializer lists.

As this is "only" a fuzzer, performance is not really critical, but
still has some impact on the efficiency of the whole fuzzer.
That said, this CL is mostly a cleanup to replace unwanted code pattern
by better code.

R=jkummerow@chromium.org

Change-Id: I924c15e5d64ed584fc96c85715eef1dca5aef150
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2249928
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68413}