Add dual-sequence overloads to transform_inclusive_scan() and transform_exclusive_scan()

[jgopel]

There are dual-sequence overloads for transform() (this overload is called zip in may other languages) and transform_reduce(), in the standard, but there is no similar version for transform_inclusive_scan() or transform_exclusive_scan(). This patch-set also adds constexpr support to the existing overloads.

h/t to @elbeno for suggesting implementing this.