With C++14, we can make {ElementSizeLog2Of} constexpr and use it to
compute the loaded or stored memory size instead of duplicating that
information.

The code does not get shorter this way, but more robust.

R=ahaas@chromium.org

Bug: v8:9810
Change-Id: Idb7e861f833798e181694cda0db21ef57804d3a2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1914215Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64948}