change handling of const pointers in SysCopyHandle, const-retrieve in OverlapRemovalAlg

Essentially I now need to include the const modifier directly in the template type. The idea is that this allows future iterations of the handle to do different things based on whether they will provide read access or update access.

The change to OverlapRemovalAlg fixes a bug introduced in !55866 (merged), and is anyways what ought to be done.