[Executors][Distributed] custom executors for distributed actor

[ktoso]

Distributed actors must also be able to have custom executors.

I'll cleanup the code duplication for the synthesis a little bit, as it is copied from the Actor synthesis right now.

Resolves rdar://84054793

[ktoso]

• All of the synthesis code is pretty much 1:1 same as in an Actor, I'll refactor so we can share that code.

[ktoso]

Leaving this duplicated for now since we might want to change it a little bit actually for distributed -- pending discussion in evolution.

[ktoso]

(turns out having it separate was a good idea)

[ktoso]

@swift-ci please smoke test

[ktoso]

I'm very confused how this can be failing on some CI platforms but also work locally on M1 just fine 🤔 There's nothing platform specific in these changes... Trying to figure it out.

[ktoso]

Wait a moment...

Traceback (most recent call last):
  File "/home/build-user/swift/utils/PathSanitizingFileCheck", line 100, in <module>
    exit(main())
  File "/home/build-user/swift/utils/PathSanitizingFileCheck", line 74, in main
    stdin = io.open(sys.stdin.fileno(), 'r', encoding='utf-8', errors='ignore').read()
MemoryError

[ktoso]

@swift-ci please smoke test

[ktoso]

@swift-ci please smoke test

[ktoso]

@swift-ci please smoke test

[ktoso]

Missed to implement calling the initialize() in non default case; that's simple, will do in the morning

[ktoso]

@swift-ci please smoke test

[ktoso]

I have discussed the implementation approach with @rjmccall and we agreed on adding the NonDefaultDistributedActor piece of data. We may be able to streamline it afterwards; but it effectively adds the same amount of data "chunk" as the DefaultActor bit does to distributed non-default actors.

[ktoso]

Fixed pending FIXME's and comments.

@swift-ci please smoke test and merge // heh, should have merged the green build and did a follow-up PR :-/

[ktoso]

@swift-ci please smoke test