This code is public on main, but not on 6.2, so if one compiles a binary for 6.2
on main and then attempts to use a stdlib from a 6.2 aligned macOS, one gets an
ABI error since the type isn't there. Just mark these types as being available
in 6.3 so that way this is future proofed and allows for main binaries to run
against a 6.2 aligned macOS stdlib.
If you use SwiftStdlibCurrentOS availability, you will be able to
use new types and functions from within the implementation. This
works by, when appropriate, building with the CurrentOS availability
set to the current deployment target.
rdar://150944675
EventableExecutor is being removed, for now, but hopefully will
return in some form in the future.
The `asSchedulable` implementation needs to change for reasons of
ABI stability.
rdar://141348916
Reorganise the Concurrency code so that it's possible to completely
implement executors (both main and global) in Swift.
Provide API to choose the desired executors for your application.
Also make `Task.Sleep` wait using the current executor, not the global
executor, and expose APIs on `Clock` to allow for conversion between
time bases.
rdar://141348916
