FRAME: should export hash function that uses the host functions instead of pure-wasm implementation

[gui1117]

In this PR #12158 I see frame-support is re-exporting some hash function with sp_crypto_hashing, I guess it should re-export hash function that uses the host function as they are faster.

Or maybe sp_crypto_hashing should automatically use the host function as an optimization when running inside the runtime.

[Kanasjnr]

Yeah this tracks after removing the old sp_core hashing re-exports in #12158, so frame::hashing now pulls the free functions from sp_crypto_hashing, which is the pure wasm path.

The trait stuff (BlakeTwo256 / Keccak256) already goes through sp_io, so that part should be fine, i think It's mainly blake2_256 / twox_128 / etc. that people get from frame::hashing.

maybe we can have FRAME re-export sp_io::hashing for those, rather than making sp_crypto_hashing know about host functions. i can open a pr on this issue if that sounds right.