Support for Swift Testing

[johanblumenberg]

• [x] I have read the CONTRIBUTING.

🔗 Closing issues

This closes #132

📖 Summary

Support for Swift Testing

Inspired by Cuckoo

The implementation is checking if XCTest or Testing can be imported, and choses implementation based on that. In most cases though, both test frameworks can be imported, and the test failure will be reported to both.

The second commit solves a conflict between MockSwift.Predicate and Foundation.Predicate, by namespacing the type where used.