Instead of copying an array of fixed values into an std::vector for
each usage of the FOR_INPUTS macro, just iterate the constant data
directly.
This also makes the <type>_vector() functions return {constexpr Vector}
instead of {std::vector}.

R=tebbi@chromium.org

Change-Id: Ifc3e5509b2fbf5e383c967c2f46acf2b07f7b5b4
Reviewed-on: https://chromium-review.googlesource.com/725427Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48688}