This adjusts parsing of negative numbers in UnaryExpression and
MultiplicativeExpression to return double if the token is -0.

R=clemensb@chromium.org
TEST=mjsunit/regress/regress-6838-4
BUG=v8:6838

Change-Id: I6c2113b520c3831f4a5101f0a963f49c1eb9d7d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2007272Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Emanuel Ziegler <ecmziegler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65862}