panelset: Gouped panelset syncing, and support for quarto slides

[gadenbuie]

• Brings quarto-style group syncing to panelset!

• Full support for Quarto slides

• Accessibility and keyboard navigation improvements

• Much refactoring and more documentation

[codecov[bot]]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (6d7b6d9) 52.51% compared to head (df3cef0) 52.33%.

:exclamation: Current head df3cef0 differs from pull request most recent head 2db1b96. Consider uploading reports for the commit 2db1b96 to get more accurate results

Files	Patch %	Lines
R/panelset.R	42.85%	12 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #195 +/- ## ========================================== - Coverage 52.51% 52.33% -0.19% ========================================== Files 20 20 Lines 794 814 +20 ========================================== + Hits 417 426 +9 - Misses 377 388 +11 ```

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