Fixes#30403.
Having tabIndex set to 0 led to keyboard focus being put on
a scrollbar container, which led to users having to tab twice
to skip a container.
This commit also removes instances of tabIndex being set to
-1 programatically for certain cases, since it is -1 by default now.
This commit also removes `outline: none` for simplebar since
that property is not needed anymore because the wrapper is
not focusable anymore.
This refactors popover list structure to use a flattened `ul > li`
structure along with aria-related additions, enabling screen reader
accessibility and announcing menu length and position (`# of n`).
Added ARIA roles:
- `role="menu"` to the parent `<ul>` element, indicating it is a widget
offering a list of choices.
- `role="menuitem"`, `role="menuitemcheckbox"`,
or`role="menuitemradio"` to child elements based on their function.
- `role="none"` to `<li>` elements, removing the implied `listitem`
role that conflicts with the parent menu structure.
Shubham Padia
Sayam Samal