IF: Host function to set active finalizer set

[arhag]

Depends on #1509.

One new host function called set_finalizers should be added upon the activation of the IF protocol feature.

[arhag]

Progress started with code in https://github.com/fcecin/leap/commits/74295f20142ef415d6e118701777f12a7937f187.

[arhag]

The structure provided to the host function (typically referred to as the "finalizer set") should include:

• uint64_t threshold
• std::vector of structs that each contain:
  • finalizer_key which is a BLS public key
  • uint64_t weight (check that this is not zero)
  • std::string description (this is intended to hold the name of the producer using this finalizer key)

The host function should ensure that the finalizer_key is unique within the std::vector. It should also add all weights and ensure that the threshold is greater than half the total weight.

The threshold value is used instead of assuming a hard-coded number of 15 as is currently done in the code: #1536 (comment).

Also, the size of the std::vector should be used instead of assuming a hard-coded number of 21 as is currently done in the code: #1536 (comment)