Add NSRange/Range conversion API support on Linux

[gjcairo]

Currently trying to do things like the following only work on Darwin:

let swiftRange = Range(range, in: string)
                         | `- error: initializer 'init(_:in:)' requires that 'NSRange' (aka '_NSRange') conform to 'RangeExpression'

It's possible to work around this by, for example, creating the Range manually:

let start = string.utf16.index(string.startIndex, offsetBy: range.location)
let end = string.utf16.index(start, offsetBy: range.length)
let swiftRange = start ..< end

But it would be great to have full conversion support between NSRange and Swift.Range on Linux too.

[parkera]

Out of curiosity, what's your use case for NSRange on Linux? Do you find yourself having to use NSString API instead of `String?

[jmschonfeld]

Additionally, AFAICT this initializer does exist on Linux (I've tried both the nightly-jammy and nightly ubi9 image):

  1> import Foundation
  2> let nsRange = NSRange(location: 0, length: 2)
nsRange: Foundation.NSRange = {
  location = 0
  length = 2
}
  3> let string = "Hello"
string: String = "Hello"
  4> let swiftRange = Range(nsRange, in: string)
swiftRange: Range<String.Index>? = some {
  lowerBound = 0[any]
  upperBound = 2[any]
}

If you have a need for this API and are still having issues, can you attach your full reproducing code along with your environment (platform and swift version)?