* Replace stdlib and test/stdlib 9999 availability.
macOS 9999 -> macOS 10.15
iOS 9999 -> iOS 13
tvOS 9999 -> tvOS 13
watchOS 9999 -> watchOS 6
* Restore the pre-10.15 version of public init?(_: NSRange, in: __shared String)
We need this to allow master to work on 10.14 systems (in particular, to allow PR testing to work correctly without disabling back-deployment tests).
The `ObjectIdentifier(object as AnyObject)` is not necessarily stable; this breaks reflexivity for ==, and it makes the hash encoding nondeterministic.
This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.