... ,test-fast-dtoa, test-fixed-dtoa} to unittests/base/
{bignum-dtoa-unittest, dtoa-unittest, fast-dtoa-unittest,
fixed-dtoa-unittest}.

This CL also moves cctest/{gay-fixed, gay-precision,
gay-shortest} to unittest/{gay-fixed, gay-precision,
gay-shortest}.

Bug: v8:12781
Change-Id: Id6072f92908ad3abfe683c69dac041227de2553f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3607114
Commit-Queue: 王澳 <wangao.james@bytedance.com>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80572}