Revise View3DWidget save behavior for FileSystemProviders
Revise View3DWidget save behavior for FileSystemProviders

 - Fixes #111335412 - Part is deleted from Downloads after Edit>Save
 - Fixes #111379492 - Data loss and confusing file duplication when editing STLs in FileSystemProviders folders

MatterHackers/MatterControl,jlewin/MatterControl,jlewin/MatterControl,tellingmachine/MatterControl,jlewin/MatterControl,MatterHackers/MatterControl,CodeMangler/MatterControl,unlimitedbacon/MatterControl,rytz/MatterControl,unlimitedbacon/MatterControl,rytz/MatterControl,jlewin/MatterControl,mmoening/MatterControl,mmoening/MatterControl,larsbrubaker/MatterControl,unlimitedbacon/MatterControl,larsbrubaker/MatterControl,larsbrubaker/MatterControl,rytz/MatterControl,unlimitedbacon/MatterControl,tellingmachine/MatterControl,larsbrubaker/MatterControl,CodeMangler/MatterControl,mmoening/MatterControl,MatterHackers/MatterControl,CodeMangler/MatterControl