Consider making `_DAOStarFinderCatalog` and `_StarFinderKernel` public

[emolter]

We wanted to use some photutils functionality in the jwst repository to avoid repeating code. See spacetelescope/jwst#9671 for details of that attempted refactor.

Specifically, the goal was to replace the JWST source catalog's methods for computing DAOFind sharpness and roundness with photutils methods, as well as to use photutils for handling the DAOFind kernel and making the cutouts.

The JWST source catalog uses a segmentation algorithm by default, so we didn't want to inherit the whole DAOStarFinder, just some methods - and even if we did use DAOStarFinder as a parent class, it doesn't have direct access to the necessary sharpness and roundness1 methods: only the private _DAOStarFinderCatalog has them.

Would you consider making _DAOStarFinderCatalog and _StarFinderKernel public (or making their methods accessible via public API in some other way) such that we could re-use photutils methods instead of maintaining our own versions?