This makes ClangImporter automatically conform C++ collection types to `Cxx.CxxRandomAccessCollection` protocol.
We consider a C++ sequence type to be a random access collection type its iterator conforms to `UnsafeCxxRandomAccessIterator`.
This lifts the requirement for the user to explicitly add `import Cxx` in Swift code that relies on protocols from the `Cxx` module, such as `CxxSequence`.
To determine whether to conform a C++ type to `CxxSequence` protocol automatically, ClangImporter checks if the corresponding iterator type conforms to `UnsafeCxxInputIterator`.
This logic had false-positives, e.g. `Optional<OpaquePointer>` was treated as if it conforms to `UnsafeCxxInputIterator` while it actually doesn't. This happened because `lookupConformance` returned a conformance with a conditional requirement (`Wrapped : UnsafeCxxInputIterator`) that is not satisfied for `OpaquePointer`.
rdar://100265664
This makes ClangImporter automatically conform C++ sequence types to `Cxx.CxxSequence` protocol.
We consider a C++ type to be a sequence type if it defines `begin()` & `end()` methods that return iterators of the same type which conforms to `UnsafeCxxInputIterator`.
