[cxx-interop] Import iterator dereference operators

[egorzhdan]

C++ iterator dereference operator is mapped to a Swift computed property called pointee.

For example:

struct ConstIterator {
  // ...
  const int &operator*() const { /* ... */ }
};

is imported as

struct ConstIterator {
  var pointee: Int32 { get }
  @available(*, unavailable, message: "use .pointee property")
  func __operatorStar() -> UnsafePointer<Int32>
}

[egorzhdan]

@swift-ci please smoke test

[egorzhdan]

Side note: ImportDecl.cpp is way too big, I'll move the decl synthesis logic into a separate file in another PR.

[egorzhdan]

@swift-ci please smoke test

[Huddie]

This looks great! One naming question: Is operator*() known as an iterator dereference or just "dereference" ? Sounds like if a class has operator*() its by def an Iterator, just want to confirm thats the case

[egorzhdan]

Hmm, I can't find the conventional name of this operator in C++ reference.
operator*() is sometimes also defined for custom pointers, e.g. std::unique_ptr. However, we might want to prohibit using those types from Swift. I think the only valid use case of operator*() from Swift is iterator dereferencing (but I might be missing something).

[egorzhdan]

Actually that's a good point @Huddie. Calling operator*() "iterator dereference" is probably not always correct, I'll adjust the naming. Thanks!

[egorzhdan]

@swift-ci please smoke test

[zoecarver]

Lovely, as per usual :)