Part of meta-ticket #32414.

Deprecating is_FiniteField, is_PrimeFiniteField, and is_FiniteFieldElement is done for uniformity but is not needed to support modularization. #32432 shows that sage.rings.finite_rings.finite_field_base (which defines the ABC FiniteField) can be imported without pulling in implementation classes.

sage.rings.finite_rings must become a namespace package because element implementations depend on various libraries.

CC: @dimpase @kwankyu @fchapoton @tscrim

Component: refactoring

Author: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/32664