validator set precompile

[igorcrevar]

Description

Validator set pre-compile will provide two functions to smart contracts:

• isValidator(address) bool
• hasQuorum(address[]) bool

Precompile will work only for polybft consensus and will not provide any of those two functions at genesis time

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Documentation update

I think we should add this to the docs