Refactor PatchWSIDataset #3930
Description
Currently, PatchWSIDataset lives in monai/app and works only with WSIReader for specific pathology use-cases. In our effort to blend this component in MONAI core, it can be extended to use any derivative of ImageReader class; however, some considerations are required to avoid unnecessary caching for backend libraries with intrinsic cache (like OpenSlide). Moreover, reading a subregion needed to be handled separately for non-WSI reader classes.
P.S. will be discussed with pathology WG to explore more pathology use-cases.