* refactor(aio): use explicit CSS class for TOC container
This makes the styling less fragile to changes in the HTML
* fix(aio): schedule TocComponent.activeIndex updates via AsapScheduler
We use the `asap` scheduler because updates to `activeItemIndex` are triggered by DOM changes,
which, in turn, are caused by the rendering that happened due to a ChangeDetection.
Without asap, we would be updating the model while still in a ChangeDetection handler,
which is disallowed by Angular.
* refactor(aio): do not instantiate floating ToC if not displayed
* feat(aio): display the h1 at the top of the floating TOC
Closes#16900
* refactor(aio): combine the TOC booleans flags into a "type" state
* refactor(aio): remove unnecessary `hostElement` property
* fix(aio): ensure that transition works on TOC
* fix(aio): use strict equality in ToC template
- Use buttons for the TOC “Contents” label when embedded-and-expandable or TOC on the right to satisfy a11y.
- Add aria-pressed setting for the toggles in TOC and NavItem.
- Clicking the right panel TOC “Contents” button scrolls to top.
- When embedded use same rotating caret as sidebar
- When embedded and no secondaries, “Content” is just a label.
- Gray background for focused buttons rather than outline because can’t get carets to work with outline.
TOC appears in right panel when wide and hides embedded TOC
Right TOC panel height adjusts dynamically during scroll
Refactored `TocService` and its tests for clarity.
