SR.series should simplify its terms

[rwst]

series should simplify its terms on a per-term basis:

sage: var('x,y')
(x, y)
sage: ex=1/(1-x*y-x^2)
sage: ex.series(x,5)
1 + (y)*x + (y^2 + 1)*x^2 + ((y^2 + 1)*y + y)*x^3 + (((y^2 + 1)*y + y)*y + y^2 + 1)*x^4 + Order(x^5)

Compare with e.g. Pari:

? 1/(1-x*y-x^2) + O(x^5)
%1 = 1 + y*x + (y^2 + 1)*x^2 + (y^3 + 2*y)*x^3 + (y^4 + 3*y^2 + 1)*x^4 + O(x^5)

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/16213

[rwst]

comment:3

Will be fixed in #17400.