Also, fix the implementation of {operator==} and add {operator!=}.
{operator==} could not be instantiated on a {Vector<T>} where T is not
const, as it would access the fields of another instantiation of Vector
({T} vs {const T}).

R=jkummerow@chromium.org

Bug: v8:9810
Change-Id: I65c2d3071a781f6fe7a624b727d2770b43b7f7a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1932363
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65155}