Log message:
python/wheel.mk: simplify a lot, and switch to 'installer' for installation

This follows the recommended bootstrap method (flit_core, build, installer).

However, installer installs different files than pip, so update PLISTs
for all packages using wheel.mk and bump their PKGREVISIONs.

Log message:
py-jupyter_packaging: added version 0.12.3

Tools to help build and install Jupyter Python packages that require a
pre-build step that may include JavaScript build steps.