Re-enable PDF builds for Read the Docs

[agriyakhetarpal]

Description

The SVG images generated by the sphinxext/inheritance_diagram.py extension create multiple PDFs upon LaTeX output with Sphinx's LaTeXBuilder. This PR makes them render on HTML output only, which is in-line with documentation for other projects that display inheritance diagrams for API components.

Closes #3240

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (67dcb1c) 99.71% compared to head (cac25b1) 99.71%.
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3260   +/-   ##
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  Coverage    99.71%   99.71%           
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  Files          248      248           
  Lines        18861    18861           
========================================
  Hits         18807    18807           
  Misses          54       54           

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[Saransh-cpp]

Awesome, looks good, thanks @agriyakhetarpal!

[agriyakhetarpal]

I also added a few CSS improvements and removed rules we did not need (we can inherit them from the theme itself). Ready to merge now