Add ABI checking test for Distributed

[ktoso]

We did once accidentally break ABI and it caused all kinds of trouble in undoing it since it was rather late.

We should have ABI testing, which this PR adds.

Resolves rdar://106067256

[ktoso]

I prepared a digester dump using: ``

However struggle to figure out how to make sure the digester invocation sees the distributed module 🤔 I guess it is not in the dummy sdk, but how would I get it there or otherwise visible 🤔

/Users/ktoso/code/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/bin/swift-api-digester -target arm64-apple-macosx10.13 -diagnose-sdk -module Distributed -o /Users/ktoso/code/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/test-macosx-arm64/api-digester/Output/stability-distributed-abi.test.tmp.tmp/changes.txt -module-cache-path /Users/ktoso/code/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/test-macosx-arm64/api-digester/Output/stability-distributed-abi.test.tmp.tmp/module-cache -sdk /Users/ktoso/code/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/test-macosx-arm64/api-digester/Output/stability-distributed-abi.test.tmp.tmp/dummy.sdk -abi -avoid-location

<unknown>:0: warning: no such sysroot directory: '/Users/ktoso/code/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/test-macosx-arm64/api-digester/Output/stability-distributed-abi.test.tmp.tmp/dummy.sdk'
<unknown>:0: warning: using sysroot for 'dummy' but targeting 'MacOSX'
<unknown>:0: error: cannot load underlying module for 'Darwin'
Failed to load module: Distributed

Any hints welcome, thansk!

[ktoso]

Superseded by #71911