Direct use of "setup.py sdist" is deprecated. Instead we use build to create the sdists.
We add new targets make sagemath_objects-sdist etc.
We move targets make pypi-sdists (which now uses the new targets), make wheel, and make pypi-wheels from the top-level Makefile to build/make/Makefile.in. This improves make pypi-wheels: It no longer builds the sagemath-objects wheel multiple times (as dependencies of other packages).
Depends on #34858
CC: @kiwifb
Component: build
Author: Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/34855