ERC-7766: Signature Aggregation for Account Abstraction

The core ERC-4337 previously included the specification for signature aggregation.
However, as this feature is not required for the functioning of the Account Abstraction, it is being extracted from the core ERC-4337 into a standalone specification.
This specification is currently identical to the one previously implemented in ERC-4337 and does not require any modifications to the deployed ERC-4337 contracts.
However, being a standalone proposal, “ERC-7766: Signature Aggregation” will continue evolving separately from ERC-4337 on its own timeline.

This is the PR to create the new ERC:

This is the PR to remove the Signature Aggregation specification from ERC-4337: