[Framework] Provide a new seed function in simple_rng that allow developers to define a nonce or index

[jolestar]

Proposal Details

Provide a new seed function in simple_rng that allows developers to define a nonce or index.

Such as:

public fun rand_u64(): u64;
public fun rand_u64_with_index(index: u64): u64;

If a developer calls rand_u64 multiple times rand_u64 in a transaction, he will get the same rand number. So he should call rand_u64_with_index.

cc @mx819812523 @yubing744