python: Add proper support for pyproject.toml-based builds

python: Add proper support for pyproject.toml-based builds

This removes the changes made in
61f202c0170785addbbc449e4de61cc5886f0833 and adds actual support for
pyproject.toml-based (PEP 517) builds of Python packages.

Packages can force the use of the old build process by setting
PYTHON3_PKG_FORCE_DISTUTILS_SETUP:=1; this should only be a temporary
workaround until the package can be updated/fixed to use the new build
process.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>
(cherry picked from commit 5156c0c82bcb18481bf588ba4b1ff67c12422a80)