[cxx-interop] Check the presence of copy constructor correctly

This removes a longstanding workaround in the import logic for C++ structs:
Swift assumed that if a C++ struct has no copy constructor that is explicitly deleted, then the struct is copyable. This is not actually correct. This replaces the workaround with a proper check for the presence of a C++ copy constructor.

Author: egorzhdan

lib/ClangImporter/ClangImporter.cpp

@@ -7491,8 +7491,9 @@ static bool hasCopyTypeOperations(const clang::CXXRecordDecl *decl) {
       }))
     return false;
 
-  // TODO: this should probably check to make sure we actually have a copy ctor.
-  return true;
+  return llvm::any_of(decl->ctors(), [](clang::CXXConstructorDecl *ctor) {
+    return ctor->isCopyConstructor();
+  });
 }
 
 static bool hasMoveTypeOperations(const clang::CXXRecordDecl *decl) {