2806: Remove all imports of deprecated imp module

[krzywon]

Description

This removes all references to the imp module that has been deprecated since Python v3.4 and fully removed in Python v3.12, in favor of importlib resources. The old module was still in three places, GuiUtils (unused), build_sphinx (breaking py3.12), and run_one (used occasionally).

Fixes #2806

How Has This Been Tested?

The docs build, and running a single test file with run_one succeeds.

Review Checklist (please remove items if they don't apply):

• Code has been reviewed
• Functionality has been tested
• Windows installer (GH artifact) has been tested (installed and worked)
• MacOSX installer (GH artifact) has been tested (installed and worked)

[rozyczko]

Exactly what stackoverflow says should be done.
Changes look good.

There is still a reference to imp in MainWindow\PackageGatherer. Should it be removed?

[krzywon]

Exactly what stackoverflow says should be done.

I feel called out...

There is still a reference to imp in MainWindow\PackageGatherer. Should it be removed?

Yes. I'll look into it.

[butlerpd]

Should this also be against 6.0.0?

[butlerpd]

@wpotrzebowski to check for mac compatibility