This ticket adds EllipticCurveHom_scalar, a new class encapsulating scalar multiplications on elliptic curves. This serves two main purposes:

1. It solves one of the motivations behind Make EllipticCurveIsogeny objects faster to create via lazy evaluation #8014 (faster multiplication_by_m_isogeny).
2. Wrapping scalar multiplications as an EllipticCurveHom is an important step towards implementing endomorphism rings (see Meta-ticket: Further work on isogenies and endomorphisms of elliptic curves #7368).

We also deprecate .multiplication_by_m_isogeny(): It should be replaceable by .scalar_multiplication() in all cases.

Depends on #32502
Depends on #32744
Depends on #33865

CC: @defeo @JohnCremona @tscrim @videlec @fchapoton @kwankyu

Component: elliptic curves

Author: Lorenz Panny

Branch/Commit: 884263e

Reviewer: John Cremona

Issue created by migration from https://trac.sagemath.org/ticket/32826