WIP: Use platformdirs package for all user-related file paths

[krzywon]

Description

This is a WIP. This uses the platformdirs package for os agnostic pathing to store log files, configurations, and app data. This was suggested by @llimeht in the wheels discussion in #3161. This automatically creates subfolders for each version so new configs/docs/etc no longer require versioning in their filename and/or paths, which has been removed here.

Still left to do:

• Copy plugin models and configs from old locations to new locations (if possible) (others that may be useful - categories)
• Test on multiple OSes (Windows seems okay so far...)
• Documenting the new locations
• Add methods to open user file location(s)
• Include platformdirs in requirements.txt(?) - I already had it in my environment, so this may not be needed
• Should this be against v6.0.1 or v6.1.0?
• Fix installer builds (remove log.ini from files lists)

How Has This Been Tested?

Ran SasView from source (Windows 11) and verified the new file locations are being used instead of the user directory.

Review Checklist:

Documentation (check at least one)

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• This will affect the installers
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)

Licencing (untick if necessary)

• The introduced changes comply with SasView license (BSD 3-Clause)