BL12-381 Integration

[PlamenHristov]

What

Added:

• BLS12_G1ADD
• BLS12_G1MUL
• BLS12_G1MULTIEXP
• BLS12_G2ADD
• BLS12_G2MUL
• BLS12_G2MULTIEXP

Missing:

• BLS12_PAIRING
• BLS12_MAP_FP_TO_G1
• BLS12_MAP_FP2_TO_G2
• BLS12_HASH_TO_G1
• BLS12_HASH_TO_G2

Why

Because of issue #779

Known limitations

• Missing tests
• Panics if points are invalid
• Implementation is likely to be imperfect

[jayz22]

Some general comments. I'm not too familiar with the implementation details yet.

None of these functions can use existing metering cost types, for each of these functions {p1, p2}_{add, mul, serialize}, a new cost types need to be added, calibrated and charged.
(I also remember @graydon mentioned something we need to be careful about when it comes to FFI, but I can't recall exactly)
These functions need to be exposed via the env, via env.json entry and a corresponding implementation in host.rs.
It would be nice to have some tests, not comprehensive coverage but for sanity checks, to make sure they are doing what's expected and there are no obvious issues.

[dmkozh]

Besides the points that @jayz22 has mentioned, there are important high-level issues:

• Modifying the env is a protocol change and I'm not sure we have a proper mechanism for protocol-gating the env functions yet (to be more specific, we could bump env common to protocol 21, but I'm not sure that's the way to go, given that we might still want to do non-breaking protocol 20 changes)
• Panics are not acceptable

I suppose this PR could be used as a starting point for the future work, but we can't really merge it until these issues have been resolved.

[PlamenHristov]

Ok I think I know what needs to be done to the PR to make it review ready. Will convert to draft in the meantime

[PlamenHristov]

1. Implemented the missing:

• BLS12_PAIRING
• BLS12_MAP_FP_TO_G1
• BLS12_MAP_FP2_TO_G2
• BLS12_HASH_TO_G1
• BLS12_HASH_TO_G2

2. Added tests

Ready for review in terms of the implementation.

Still requires adding budgeting of individual operations and charging them in stellar-xdr