Make `BlockNumberProvider::set_block_number` available in tests / std (#3974)
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. --------- Co-authored-by: Bastian Köcher <[email protected]> Co-authored-by: Oliver Tale-Yazdi <[email protected]>