fignum_exists() could handle string numbers? #2880

It is possible to create a figure with a string "number": figure(num="Charts"), which is used as the window title (if any).

This string number is even recognized by pyplot.subplots(…, num="Charts"): it does recover the original figure and axes.

However, pyplot.fignum_exists("Chart") returns False.

So, part of Matplotlib knows that a figure was created (and is open) with a certain string "number" (subplots(),…), while another part of Matplotlib doesn't (fignum_exists()). It would be useful if fignum_exists() was aware of figure string numbers too.