devel/py-importlib-metadata: add explicit setuptools BUILD_DEPENDS

Per PEP-518 [0], for projects using setuptools as the build backend,
both setuptools and wheel are to be specified, as wheel is a plugin
for setuptools to support the format at all. Additionally, wheel
itself will soon [1] not depend on setuptools, but rather the
dependency tree will reverse.

With hat: python
Approved by: mentors (implicit), swills (maintainer, implicit)
References: https://peps.python.org/pep-0518/#build-system-table [0]

		https://github.com/pypa/wheel/pull/501 [1]