This function is currently only exposed to runtime-benchmarks, where it
should be available in all tests.

Also made it available in `std` because this is how `set_block_number`
works in FRAME System, however, not sure if it is needed in the latest
std/no_std paradigm.

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Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>