pkg_resources use discouraged

[DougBurke]

setuptools 67.5.0 (released 05 Mar 2023) has this to say

Although pkg_resources has been discouraged for use, some projects still consider pkg_resources viable for usage. This change makes it clear that pkg_resources should not be used, emitting a DeprecationWarning when imported.

linked to pypa/setuptools#3843

We have one use case -

sherpa/sherpa/utils/formatting.py

Lines 29 to 39 in 859455d

	import pkg_resources
	import numpy as np
	# Used by printoptions
	DISPLAY_WIDTH = 80
	# The CSS file for the Notebook HTML code
	CSS_FILE_PATH = "/".join(("static", "css", "style.css"))
	CSS_STYLE = pkg_resources.resource_string("sherpa", CSS_FILE_PATH).decode("utf8")

[DougBurke]

This is part of #1342 but I'll keep it as we can deal with pkg_resources separately from what we want to do about __file__.

[DougBurke]

The replacement is easy - as we now require python > 3.7

https://importlib-resources.readthedocs.io/en/latest/migration.html#pkg-resources-resource-string