Explanation: Fixes an issue where the generated reverse interop header
would not compile for nested classes when library evolution is turned
off.
Scope: C++ reverse interop for nested classes for non-opaque types.
Issue: rdar://147882976
Risk: Low, the fix is fairly targeted. While it does affect other
(non-nested type) scenarios, those changes are fairly straightforward
making some names fully qualified. Moreover, that is well tested in our
test suite.
Testing: Added tests to test suite
Reviewer: @egorzhdan