std.algorithm.iteration.each can now be called with a lambda taking >2
args. This should work for any input range that returns a tuple and any
type with a non-templated opApply that takes a multi-arg delegate.

Determining the arity of a templated opApply still poses a problem, so
that case is not supported.

This also adds support for `each` with two ref args.

When given a binary function that takes two args by ref,
std.algorithm.iteration.each should use both args by ref.

It was previously discarding ref on the first arg, assuming it was for
an index.

Resolves #15358.

Improve std.algorithm.iteration.each