gh-36794: `sage --package create --pypi`: Create a wheel package by default if possible
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We change the default of `sage --package create --pypi` to create a
wheel package (if the package has a platform-independent wheel on PyPI)
instead of a normal package (built from source).
This is simpler (no spkg-install.in script, no build dependencies) and a
bit faster.
As an illustration, we change one SPKG, `six`, from normal to wheel.
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URL: https://github.com/sagemath/sage/pull/36794
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe
