Fix auto-scroll undershooting correction location on initial page load

Summary

Bug: Navigating to an anchor link on docs with images causes the initial auto-scroll to "undershoot" the correct location. This is because the scroll location is calculated prior to the images loading, so the image heights aren't accounted for in the location calculation.

Fix: Wait for the document to finish loading and then scroll to the location. After scrolling to the location, call el.scrollIntoView() as a backup.

Additional Bug: Auto-scroll on an initial page load does not scroll the appropriate sidebar item into view. This is because #highlight() is blocked while the Tweezer animation is running and will not scroll the sidebar if the item is already active.

Fix: Call #highlight() after the Tweezer scroll animation is complete with a parameter to force the scroll.

Related issue, if any:

https://github.com/docsifyjs/docsify/issues/351 https://github.com/docsifyjs/docsify/issues/559

What kind of change does this PR introduce?

Bugfix

For any code change,

[ ] Related documentation has been updated, if needed
[ ] Related tests have been added or updated, if needed

Does this PR introduce a breaking change?

Tested in the following browsers:

[x] Chrome
[x] Firefox
[ ] Safari
[x] Edge

docsifyjs / docsify