We already have something called "module interfaces" -- it's the
generated interface view that you can see in Xcode, the interface
that's meant for developers using a library. Of course, that's also a
textual format. To reduce confusion, rename the new module stability
feature to "parseable [module] interfaces".
* [InterfaceGen] Only print 'mutating' and 'nonmutating' on accessors
* Add SILGen test for usage of dynamic accessors in and out of interfaces
* Add -enable-objc-interop to dynamic_accessors test
