Use strongSelf instead of `self`
Use strongSelf instead of `self`

1.) Prevent using `self` which is relying on a compiler bug: https://github.com/apple/swift-evolution/blob/master/proposals/0079-upgrade-self-from-weak-to-strong.md#relying-on-a-compiler-bug
2.) Unwrapping self by using strongSelf is used already in other places in the project so this will make the code consistent across the project.

parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,e78l/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,parkera/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,parkera/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,parkera/swift-corelibs-foundation