Interop: Set Swift interop flag for Xcode 15

In the Xcode 15 Beta, the swiftc compiler no longer accepts the
experimental version of this flag.

Author: ADKaster

Interop/Sources/Swift/Executable/CMakeLists.txt

@@ -1,6 +1,6 @@
 add_executable(E
   E.swift)
 target_compile_options(E PRIVATE
-  -enable-experimental-cxx-interop)
+  -cxx-interoperability-mode=default)
 target_link_libraries(E PRIVATE
   cxx_library)