Tracking issue as a continuation to gh-6166

• add copy-on-overlap to nditer, as optional flag ENH: umath: ensure ufuncs are well-defined with memory overlapping inputs #8043
• use it for ufuncs ENH: umath: ensure ufuncs are well-defined with memory overlapping inputs #8043
• check whether copy-on-overlap is respected in indexed assignment
• respect it for dot() BUG: core: in dot(), make copies if out has memory overlap with input #8539
• check other places in numpy that may need checking

Some initial code, master...pv:copy-overlap