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Following making invoke() constexpr this change also adds constexpr
support to ranges::for_each. This is done by no longer dispatching to
the std:: implementation, but rather implementing the loop ourselves.
This change furthermore reduces the delta to C++20 by using the right
return type for ranges::for_each, as well as adding an implementation of
range::for_each_n.

Bug: 1071094
Change-Id: Ic619f0c9926ef9c3e9fda4a67ab5e02bb5262402
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2325920Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792848}