Add derivative operator #32554
Description
Currently, the output of a derivative of a symbolic function has the annoying property that sagemath cannot read it back as input, for example the following does not work because D is not defined.
sage: function('f'); var('x y')
sage: diff(f(x+y),x)
D[0](f)(x + y)
sage: D[0](f)(x + 2*y)
This ticket implements such a derivative operator that fixes this inconsistency.
Component: symbolics
Author: Marius Gerbershagen
Issue created by migration from https://trac.sagemath.org/ticket/32554