RFE: Replace use of pkg_resources with importlib.metadata

[kloczek]

See discussions:
astropy/astropy#11091
pypa/pip#7413

[tkloczko@devel-g2v SRPMS]$ rpm -ql python-pyparsing | grep py$ | xargs grep pkg_resources
/usr/lib/python3.8/site-packages/pyparsing/diagram/__init__.py:from pkg_resources import resource_filename

[ptmcg]

I think the suggested changes do not support back to Py3.6, which for some reason I think is still worth supporting for pyparsing (I think maybe in the next release I'll announce that pyparsing 3.1 will be released later in 2022, and will drop support for 3.6.)

But we only explicitly use pkg_resources in one place, to locate and read the jinja2 template for the railroad diagrams. This template is only about 25 lines long, I don't see a lot of harm in just in inlining it in the railroad diagram code. Then we could just cut the use of pkg_resources and not need to come up with an equivalent.

[kloczek]

Hmm .. if it is some solution which may allow do the same without pkg_resources and would allow to detach pyparsing from setuptools (which part is pkg_resources) without breaking compatibility with Py3.6 I think that it would be worth to do that 🤔

[kloczek]

Nevertheless seruptools developer confirmed that trying find some replacement for use pkg_resources is kind of best longer term solution pypa/setuptools#3279 (so it is nothing really-so-urgent for now)

[ptmcg]

Released in 3.0.9