Extend base::Extend to support a generic range as input

This replaces the overload that takes a `base::span` and adds support
for projections, similar to `base::ToVector`. Note that this does not
update the overload that consumes a `std::vector<T>&&`, and that the
legacy `std::vector<T>&&` overload does not support projections. The
right way to implement this is to probably add an adapter to treat the
values in the range as rvalues.

Bug: 378623811
Change-Id: I95bbcd99ad12c5bccc991c1aac48f4b2bc2eba4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6015246
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1382886}