This conforms mutable C++ container types, such as `std::vector`, to `MutableCollection` via a new overlay protocol `CxxMutableRandomAccessCollection`.
rdar://134531554
This fixes the automatic `std::unordered_map` conformance to CxxDictionary on Linux. Previously `std::unordered_map::const_iterator` was not auto-conformed to UnsafeCxxInputIterator because its `operator==` is defined on a templated base class of `const_iterator`.
rdar://105220600
This helps to bridge C++ random access collections, such as `std::vector` and `std::string`, to Swift by conforming them to `Swift.RandomAccessCollection`
