In addition to inputs consisting entirely of random bits, the
bigint test shell now also generates inputs that are powers of
two (i.e. have many 0-bits) and inputs with many 1-bits.
Empirically, these kinds of inputs are more likely to flush out
corner case bugs.

Bug: v8:11515
Change-Id: Ib69f12bf215055991b028196dc54ebbc00780bae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3055292
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76729}