When a DOM node is passed to an HTML tooltip, the `title` node is only
moved if it is not already in the tooltip. Otherwise, `empty()` is used
instead of `detach()` before appending the `title` to avoid memory
leaks. If a DOM node is passed to a plain text tooltip, its text is
copied via jQuery `.text()`.
Replaces `.detach()` with `.empty()`, as `.detach()` is almost never
useful but instead leaks memory. The difference between `empty` and
`detach` is that the latter keeps all the attached jQuery events/data.
However, since we do not return the previous children, the user would
have to keep these themselves, thus they can `detach()` if necessary.
This is a port of https://github.com/twbs/bootstrap/pull/14552 to v4.
as role="menu" is a very specific (and strict) ARIA pattern for
desktop-like application menus, and our dropdowns are often used
as pure navigation dropdowns, this change abandons ARIA menus for
a more open-ended and light-weight approach
(see http://heydonworks.com/practical_aria_examples/#submenus and
http://www.w3.org/WAI/tutorials/menus/flyout/#improve-screen-reader-support-using-wai-aria)
note that in dropdown.js, switched to now target ``.dropdown-menu``
instead of ``role["menu"]`` - this also prevents bootstrap scripts
from "bleeding" into non-bootstrap components on the same page.
also removed the ``role=["listbox"]`` part, which appears to be
vestigial/unused (only place in bootstrap that uses that
role are carousels, and their key handling is done separately)
