Lower committee/validators getters price in NEO contract

[roman-khimov]

Summary or problem description
getCommittee and getNextBlockValidators calls cost (1 << 22) * ExecFeeFactor at the moment which in default configuration is 1_25829120 GAS. I think there are two problems with this value:

• it's not justified by real execution cost
  Nodes cache committee in memory, so unlike getCandidates these calls don't walk through the DB, they're more like getRegisterPrice or getGasPerBlock in terms of real execution overhead. This is true for both C# and Go implementations and any other ones are likely to do this too.
• this cost is much higher than MaxVerificationGas, so it's impossible to use these methods in verification scripts/contracts
  Both entities (committee and validators) play an important role, so there are use cases for accessing them in verification context. For example, that's the way we'd like to get NeoFS alphabet nodes for NeoFS governance by mainnet Committee #2267 implementation.

Do you have any solution you want to propose?
Change price of these calls to 1 << 16.

Neo Version

• Neo 3

Where in the software does this update applies to?

• Other: NEO native contract