nazca #234655 Add approx match distance based on diff lib [validation pending]

This is::

1.0 - difflib.SequenceMatcher(None, x, y).ratio()

prioritynormal
typeenhancement
done in0.5.0
load0.100
load left0.000
closed by#68d1ae13c3b0 [distances] Add difflib match distance, closes #234655
patch[distances] Add difflib match distance, closes #234655 [applied]