Support actor object conforming to Actor protocol

[treastrain]

Issue

Part of #216
(#216 (comment) 's "2.")

Description

Add feature generating mocks for that protocol that conform to the Actor automatically become actor.

For details: #216 (comment)

[CLAassistant]

All committers have signed the CLA.

[uhooi]

Thx PR!!

[uhooi]

I would also like you to write the following test.

/// \(String.mockAnnotation)
protocol Foo: Bar {
    func foo(arg: String) async -> Result<String, Error>
    var bar: Int { get }
}

protocol Bar: Actor {
    func baz(arg: String) async -> Result<String, Error>
    var qux: Int { get }
}

[uhooi]

@treastrain
The test is failing in Xcode 12.
Since Swift Concurrency (async/await, Actor etc) is available from Xcode 13, please skip the test in Xcode 12.

Test Suite 'MockActorTests' started at 2023-03-10 13:00:08.892
Test Case '-[MockoloTests.MockActorTests testActorProtocol]' started.
/Users/runner/work/mockolo/mockolo/Tests/MockoloTestCase.swift:154: error: -[MockoloTests.MockActorTests testActorProtocol] : XCTAssertTrue failed
Test Case '-[MockoloTests.MockActorTests testActorProtocol]' failed (1.854 seconds).
Test Suite 'MockActorTests' failed at 2023-03-10 13:00:10.746.
	 Executed 1 test, with 1 failure (0 unexpected) in 1.854 (1.854) seconds

ref: https://github.com/uber/mockolo/actions/runs/4376819642/jobs/7676406579#step:5:251

[sidepelican]

I can say the same things with #221 . See it.