Add async and throwing property support

[sidepelican]

• support for async properties? #210

Main feature

Supported { get async throws }.

/// @mockable
protocol AsyncThrowsVars {
    var getAndThrows: MyValue { get throws }
    var getAndAsync: MyValue { get async }
    var getAndAsyncAndThrows: Int { get async throws(any Error) }
}

• Generated

class AsyncThrowsVarsMock: AsyncThrowsVars {
    init() { }
    init(getAndThrows: MyValue, getAndAsync: MyValue, getAndAsyncAndThrows: Int = 0) {
        self.getAndThrowsHandler = { getAndThrows }
        self.getAndAsyncHandler = { getAndAsync }
        self.getAndAsyncAndThrowsHandler = { getAndAsyncAndThrows }
    }


    var getAndThrowsHandler: (() throws -> MyValue)?
    var getAndThrows: MyValue {
        get throws {
            if let getAndThrowsHandler = getAndThrowsHandler {
                return try getAndThrowsHandler()
            }
            fatalError("getAndThrowsHandler returns can't have a default value thus its handler must be set")
        }
    }

    var getAndAsyncHandler: (() async -> MyValue)?
    var getAndAsync: MyValue {
        get async {
            if let getAndAsyncHandler = getAndAsyncHandler {
                return await getAndAsyncHandler()
            }
            fatalError("getAndAsyncHandler returns can't have a default value thus its handler must be set")
        }
    }

    var getAndAsyncAndThrowsHandler: (() async throws(any Error) -> Int)?
    var getAndAsyncAndThrows: Int {
        get async throws(any Error) {
            if let getAndAsyncAndThrowsHandler = getAndAsyncAndThrowsHandler {
                return try await getAndAsyncAndThrowsHandler()
            }
            return 0
        }
    }
}

Side effects

• For var foo: Int { get }, since the value is never set through original protocol, the call count has been removed.

[sidepelican]

• it should be tested for generic(using associated type) property
  → mockolo already handled generic type as Any with tyepalias

[sidepelican]

throws(Never) means no throws. Without this consideration, there would be warnings in the generated code.

[sidepelican]

This block is very complicated 🤪 but mockolo handles both class and protocol here, so it has to be this way.

[sidepelican]

The computed property is generated as below, but I think it is meaningless, so I will remove it.
https://github.com/uber/mockolo/pull/267/files#diff-0680dee8c19da68e406e1ecf918c1c39fe5c55214b3e399ac8dd929fe6b72c7cL43-L48

[fummicc1]

Thank you for your PR! I will take more time to finish reviewing this PR.

[fummicc1]

Thank you so much!