[test] Allow setting blockchain's clock

[m-Peter]

Depends on: onflow/cadence#2734

Description

Implements the TestFramework.MoveTime(int64), so that users can manipulate the blockchain's time.
It passes a custom Clock implementation to the EmulatorBackend.

Example usage:

import Test

pub fun test() {
    let blockchain = Test.newEmulatorBlockchain()
    // timeDelta is the representation of 35 days,
    // in the form of seconds.
    let timeDelta = Fix64(35 * 24 * 60 * 60)
    blockchain.moveTime(by: timeDelta)
    // A negative time delta moves the time backwards
    blockchain.moveTime(by: timeDelta * -1.0)
}

---

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[turbolent]

Nice!

[SupunS]

Nice!

[m-Peter]

I would update the cadence dependency to a commit, but there's a breaking change for ReadRandom, so it wouldn't work anyway.

[m-Peter]

@SupunS I have bumped the cadence & flow-go dependencies to certain commits, so I think this is good to be merged 🙏