Malformed mock generated from `[<T>: Observable<K>]` using RxSwift

[jwsinner]

Basic reproducer:

import RxSwift

/// @mockable
protocol Testing {
    var stream: [String: Observable<Int>] { get }
}

Produces:

import RxSwift


class TestingMock: Testing {
    init() { }
    init(stream: [String: Observable<Int>]) {
        self._stream = stream
    }

    private var streamSubjectKind = 0
    private(set) var streamSubjectSetCallCount = 0
    var streamSubject = PublishSubject<Int>() { didSet { streamSubjectSetCallCount += 1 } }
    var streamReplaySubject = ReplaySubject<Int>.create(bufferSize: 1) { didSet { streamSubjectSetCallCount += 1 } }
    var streamBehaviorSubject: BehaviorSubject<Int>! { didSet { streamSubjectSetCallCount += 1 } }
    var _stream: [String: Observable<Int>! { didSet { streamSubjectSetCallCount += 1 } } // <- Malformed dictionary
    var stream: [String: Observable<Int>] {
        get {
            if streamSubjectKind == 0 {
                return streamSubject // <- Incorrect return type (same for others below aside from _stream)
            } else if streamSubjectKind == 1 {
                return streamBehaviorSubject
            } else if streamSubjectKind == 2 {
                return streamReplaySubject
            } else {
                return _stream
            }
        }
        set {
            if let val = newValue as? PublishSubject<Int> { // <- Incorrect cast
                streamSubject = val
                streamSubjectKind = 0
            } else if let val = newValue as? BehaviorSubject<Int> {
                streamBehaviorSubject = val
                streamSubjectKind = 1
            } else if let val = newValue as? ReplaySubject<Int> {
                streamReplaySubject = val
                streamSubjectKind = 2
            } else {
                _stream = newValue
                streamSubjectKind = 3
            }
        }
    }
}

I'm assuming this is related to #307. I should note that until very recently the mock being generated for something like this was

private var _streams: [String: Observable<Int>]!
    var streams: [String: Observable<Int>] {
        get { _streams }
        set { _streams = newValue }
    }

which has been working nicely. A flag to disable decomposition in the rx arguments would definitely be a nice to have.