CountableRange is deprecated, renamed to Range

[spevans]

• Replace NSRange.toCountableRange() with Range.init?(_:)

• Update Test cases.

[spevans]

@swift-ci please test

[parkera]

@airspeedswift does this line up with the changes you've been working on here too?

[airspeedswift]

Please don't make this change. I already made it originally and had to revert it, because we don't have a 5.0 branch for corelibs-foundation, so Linux testing of the 5.0 swift branch started failing.

That said, it is a good point that the toCountableRange method should be replaced by just a Range.init. But that'll break stuff too so please hold off for now. 5.0 branch will rebranch soon, then we can do it.

[airspeedswift]

DNM for now until the range changes are on swift's 4.2 branch.

[spevans]

@swift-ci please test

[airspeedswift]

Now that the conditionally-conforming Range is available on 4.2, I think this is gtm.

[spevans]

@swift-ci please test and merge