Support for Aggregate Signatures

[DrPeterVanNostrand]

Currenty, FVM exclusively supports non-aggregate signatures via its verify_signature syscall, ideally FVM would support both aggregate and non-aggregate. BLS aggregate signatures allow multiple parties to sign multiple messages with a single constant-sized signature that is more computationally efficient to verify than verification of multiple individual signatures. As non-aggregate BLS is already supported in FVM, a new syscall could be added to allow verification of aggregate signatures without altering FVM's current interface use for verifying non-aggregate signatures.

FIP: 0079 (PR #841)

[AnomalRoil]

How does this relates to #846 BTW?

From a gas cost perspective the two need to be well aligned so that the raw BLS pairing operations wouldn't be less costly than using the aggregate call.

[Stebalien]

In theory, #846 is more general purpose and could replace this FIP. However, this FIP is:

1. More convenient (it does everything).
2. Likely more efficient for bulk verification as it avoids jumping back and forth between the actor and the FVM for each message being verifies.

I'd actually prefer to just support the BLS12-381 primitives, but that's probably too slow (and also something that still needs a FIP/implementation).