Use the `%target-swift-5.X-abi-triple` substitutions to compile the tests for
deployment to the minimum OS versions required for the APIs used in the tests,
instead of disabling availability checking.
This happens to work, but is not a real fix; we are not handling well
types declared in a library evolution enabled library, which this DAS
is. Without this, at runtime, we crash in LocalTestingDAS using actor
initializers
This was benign with `Sendable`, but is not benign for the `Encodable`
and `Decodable` synthesis for distributed actors, which results in a
crash in TBD generation.
Fixes rdar://92008955.
The stored properties `id` and `actorSystem` that are synthesized for
a distributed actor would end up getting placed in fairly random
locations within the stored properties lists based on when they were
synthesized. This means that they (1) weren't always in the prefix, and
(2) weren't always the same order in every translation unit. Hilarity ensues.
Fixes rdar://92142457.
