Tabpane: support persistence of all active tabs

[chalin]

• Updates option value to disable persistence: now use persist=disabled (instead of off)
• Enhances tabpane to support the persistence of the active tab selection for all tabpanes (excluding those with persist=disabled), rather than just the last activated tab
• Restores all persisted activated tabs on page load
• Persists in localStorage a count of the tab-activated events
• Persists each activated tab in localStorage using the tab's persistence key. The value associated with the key is the tab-activated-event count plus one (also saved to localStorage). This supports typical use cases, in addition to the one explained below.
• Drops button.onclick in favor of click event handlers.

Handling of non-uniform shared tabs

Assume that a page contains three tabpanes with the following distribution of tabs A, B, C, D -- where these letters represent the tab-persistence keys:

1. A, B
2. B, D
3. A, B, C

If you activate tab B from any tabpane, it will become active in all three tabs and the selection will be persisted. If you then select C, then tab C will become active in tabpane 3, but tab panes 1 and 2 will remain active at B -- and these settings are persisted. If you then select A, then: tabpanes 1 and 3 become active at A, but tabpane 2 remains unchanged.

IMHO, this applies the principle of least surprise.

Preview and tests

• https://deploy-preview-1611--docsydocs.netlify.app/docs/adding-content/content/#custom-sections -- select yaml and refresh the page. You'll see that the choice of language persists in this page and is active in other pages with the same tab-persistence key
• https://deploy-preview-1611--docsydocs.netlify.app/docs/adding-content/shortcodes/#tabbed-panes -- select, say, German, and Scala, then refresh to see the persistence in action. Return to the previous page to see that the yaml persistence is still active.

Other

• FYI, I've successfully tested this on the OTel website.
• Updates to the changelog and docs will be made in a followup PR.

[deining]

Nice improvement! Thanks for your hard work!
LGTM, looking forward seeing this merged!
Once we manage to eventually review and incorporate long-standing PR #1202 and #1227, docsy theme will offer a really great comfort-solution for displaying ad handling tabs!

[LisaFC]

This looks really good!

[chalin]

Thanks for the reviews. As I mention in the associated issue, I'll update the tab-activation algorithm soonish, but this first version should be good enough for most sites. (I'll be fielding it soon too.)