Add a test case that checks the behaviour introduced during the refactor
of `importFunctionParameterList` and `importMethodParamsAndReturnType`.
The test checks that both Obj-C++ methods and C++ functions treat `const
T&` parameters in the same way.
The C++ interop modules require C++ support. Explicitly require C++ as
a feature when building these modules. This has no impact on the
changes as all the tests enable C++ already.
