[cxx-interop] Add flag to assume C++ types are resilient
Currently, C++ types cannot appear in resilient interfaces. There are
some cases where this is overly restrictive. We plan to improve the
logic to detect what types should not appear on resilient moduel
boundaries. In the meantime, this PR introduces a flag to disable these
errors. Users relying on this flag are on their own, this should only be
a temporary workaround until we land further improvements to this
diagnostic.
rdar://137457118