IF: copy new eosio.bios from reference-contract repo to Leap libtester and add more validations to set_finalizers host function

[linh2931]

Copy eosio.bios contract from AntelopeIO/reference-contracts#33

In addition, from @arhag in Telegram as a result of the review of AntelopeIO/reference-contracts#33

We could have overflows in f_weight_sum in set_finalizers. We should check for that in Leap.
Also, we should use check = true in Leap regardless of any assumptions we make about what the system contract may or may not do.

Continue using set as a means of detecting duplicates of public keys in set_finalizers. However, detect the duplicate early and if found throw an error where the message include the duplicate public key in its text encoding.

Either remove the operator == from bls_public_key and bls_signature or, if they are actually used, rename them equal.