Using PinnableElement in the TOC allows us to reuse styles associated with all PinnableElements, and helps ensure consistency between page tools and the TOC. This is something that would probably need to be done for T324505 anyway
Rather than updating PinnableElement to accept a class prop, I chose to rename '.sidebar-toc' to '.vector-toc', making the TOC's naming conventions consistent with the rest of Vector.
"sidebar" doesn't make sense anymore anyway, as the TOC can be in multiple locations and it's best to avoid the "sidebar" term
Bug: T324877
Change-Id: I5b9228380f5c4674ef424d33127a5cb4010822da
Collapses sub-sections in the new table of contents by default
(except for non-js and reduced-motion users) and expands the
sections when the top-level section link has been clicked.
Refactors the `activateSection` TableOfContents methods into separate
`activateSection` and `deactivateSection` functions.
Adds `expandSection` and `collapseSection` methods.
Adds triangle icon as a visual expand/collapsed indicator
next to all ToC section headings and are hidden via CSS based on
whether or not the section contains subsections.
Adds test for tableOfContents.
Bug: T299361
Change-Id: I36b3ae7f9f633877683bc17a9444c970d7fa7293
