When casting types to one another in C++, the weaker the cast,
the better.

This change replaces instances of reinterpret_cast with static_cast
or no cast where it safe and correct to do so.

BUG=angleproject:2683

Change-Id: I99c9033614a65282ae1d78cf0f4b80fabd75877a
Reviewed-on: https://chromium-review.googlesource.com/1109396
Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>