Use `assert.strictEqual`/`assert.true`/`assert.false`

`aria-haspopup="true"` is really intended to signal that an ARIA `menu` will be opened on activation. as a result, some assistive technologies will announce controls with `aria-haspopup="true"` as a menu or menu item (e.g. JAWS and NVDA).
In addition, `aria-haspopup` seems to trigger a bug in Edge/Narrator where the `aria-expanded` state is not correctly announced at the moment when `aria-haspopup` is present.
This now makes the dropdown button more like a generic disclosure widget control - see also https://www.w3.org/TR/wai-aria-practices-1.2/examples/disclosure/disclosure-navigation.html01

Be consistent with Popper's name.

Remove caret element

dropdown show method should do the same as toggle

dropdown - destroy old popper.js references

allow to pass popper.js configuration for tooltip/popover and dropdown

Backport of the unit test from https://github.com/twbs/bootstrap/pull/28928

* Don't open dropdown on ESC on trigger element

Closes #28751

* Improve code coverage for our Button plugin

* improve coverage for our Alert plugin

* test tooltip update method

* test update and dispose for dropdown

* increase code coverage requirements

* Dropdown - Allow to disable Popper.js style

* Update dropdown.js

* Update dropdown.html

* copy changes

* Close dropdown menu when focusing an outside element
* Update unit test to new markup