feat(algebra/monoid_algebra/grading): Use the new graded_algebra API (#13360)
feat(algebra/monoid_algebra/grading): Use the new graded_algebra API (#13360)

This removes `to_grades_by` and `of_grades_by`, and prefers `graded_algebra.decompose` as the canonical spelling.

This might undo some of the performance improvements in #13169, but it's not clear where to apply the analogous changes here, or whether they're really needed any more anyway,





leanprover-community/mathlib,leanprover-community/mathlib