Update dependencies for building documentation

[timmoon10]

Description

This PR updates the Sphinx-related dependencies for building docs to handle Python 3.12. I've also taken the opportunity to do miscellaneous cleanup.

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refractor

Changes

• Update dependency versions in GitHub action for docs
• Remove deprecated options from RTD theme
• Fully commit to pathlib.Path in anticipation of Sphinx 9 deprecating str paths
• Miscellaneous reorganization and cleanup

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[timmoon10]

This function was deprecated in the RTD theme 3.0.0 release: https://github.com/readthedocs/sphinx_rtd_theme/blob/7b894f5e7a5053dd35de406bc779020c229f20a9/sphinx_rtd_theme/__init__.py#L22-L26

[timmoon10]

display_version was deprecated in the RTD theme 3.0.0 release: https://sphinx-rtd-theme.readthedocs.io/en/stable/configuring.html#confval-display_version

Note that the theme no longer includes the version in the sidebar, just a pulldown menu if multiple versions are available via RTD Addons. I haven't yet thought of a good way to reproduce our hacky version pulldown menu:

TransformerEngine/docs/conf.py

Line 59 in 7681c12

Version select: <select onChange="window.location.href = this.value" onFocus="this.selectedIndex = {0}">

It seems we're not the only one affected by this change: readthedocs/sphinx_rtd_theme#1601 (comment)

[timmoon10]

Pipeline 19467512