Allow to call other contracts in verification context

[roman-khimov]

Summary or problem description
VerifyWitness helper loads verification contracts with CallFlags.ReadStates privileges (is they're not standard) which doesn't allow them to make any calls (to do that they need CallFlags.AllowCall). Now after #2215 the data that was previously available via System.Blockchain.* syscalls is only accessible via the Ledger native contract. But verification contracts can't do calls thus it's not possible at the moment to implement even the simplest verification contract that checks for blockchain height.

See #2142/#2144 also.

Do you have any solution you want to propose?
Add AllowCall to verification contract's call flags.

Neo Version

• Neo 3

Where in the software does this update applies to?

• Ledger
• Other: