Implement const operator[] in IArrayMemory interface

[konard]

Location: cpp/Platform.Memory/IArrayMemory.h:9

Current code:

//virtual TElement& operator[](std::size_t index) {}

// TODO: impl const
//virtual const TElement& operator[](std::size_t index) const {}

Issue:
The IArrayMemory interface is missing the implementation of the const version of operator[]. Currently both the regular and const versions are commented out.

Suggestion:
Implement both versions of the operator[] to provide proper const-correctness in the interface.