This improves the performance of iterating over a C++ container that is automatically conformed to `CxxConvertibleToCollection` protocol by removing the extra copy of the container.
This also tightens the requirements of `CxxConvertibleToCollection` by making `begin()` and `end()` non-mutating.
This makes `Array.init<C: CxxConvertibleToCollection>(C)` more generic by using `RangeReplaceableCollection` protocol instead of concrete `Array` type.
Since we don't automatically conform C++ non-random-access collections to `Swift.Sequence` anymore for performance reasons, we need an alternative way to access the elements of a C++ sequence from Swift.
This allows explicitly converting a C++ sequence to a Swift Array/Set.
