implementation for NSURLComponents.copy(with:)

[mbvreddy]

This PR has following:

1. Implementation for NSURLComponents.copy(with:). Approach is to create default NSURLComponent and update fields one by one.
2. Override isEqual() function. Since copy is not 'self', it is required to override isEqual to compare properties instead of object references.
3. Unit test for copy(). I've used NSURLComponents class in testcase instead of URLComponents structure because it doesn't have mapping for copy() function.

[parkera]

CFURLComponentsRef implements an equality checking function. Can we just use CFEqual?

[mbvreddy]

I tried to use it. But, couldn't figure out how to cast CFURLComponentsRef to CFTypeRef thay CFEqual expect. NSURLComponent doesn't support toll-free bridge.

[phausler]

NSURLComponents is a has-a not an is-a class so for subclasses this approach is by far safer imho

[mbvreddy]

rebased

[parkera]

@swift-ci please test linux

[CodaFi]

#590 Fixed at least one of these failures

@swift-ci please test Linux.