As a follow-up on #32566 and #32610, we replace isinstance tests with RealField_class by the sage.rings.abc.RealField.

git grep -E 'isinstance.*(Real|Complex)Field_class' finds these uses.

Depends on #32665
Depends on #32758
Depends on #32635

CC: @tobiasdiez @tscrim @EnderWannabe @bhutz

Component: refactoring

Author: Matthias Koeppe

Branch/Commit: 29e784b

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/32742