Fix active class toggling of tabs within dropdown

[cpsievert]

Closes #36947 (a regression introduced by #33079, cc @GeoSot)

As the codepen in #36947 demonstrates, when clicking on the 2nd tab in a dropdown, all the tabs within the dropdown are marked with an active class. This happens because, the current logic in _toggleDropdown() toggles the active class on the first tab within the dropdown when it shouldn't be

[GeoSot]

Looking back the commits history,
it seems that Tab was handling only the removal of active class

bootstrap/js/src/tab.js

Lines 116 to 120 in 63d38b1

	const dropdownChild = SelectorEngine.findOne(SELECTOR_DROPDOWN_ACTIVE_CHILD, active.parentNode)
	if (dropdownChild) {
	dropdownChild.classList.remove(CLASS_NAME_ACTIVE)
	}

So if we want to bring back the exact old behavior, I think it would be better to rename the const SELECTOR_DROPDOWN_ITEM, to
const SELECTOR_DROPDOWN_ITEM_ACTIVE = '.dropdown-item.active' and use it, instead of remove the handling

@cpsievert what do you think about this?

[cpsievert]

@GeoSot I don't think that's necessary since, in the new implementation, by the time we reach _toggleDropdown(), the .active class will already be added/removed from the tab via

bootstrap/js/src/tab.js

Lines 103 to 108 in 37e2e7e

	_activate(element, relatedElem) {
	if (!element) {
	return
	}
	element.classList.add(CLASS_NAME_ACTIVE)

and

bootstrap/js/src/tab.js

Lines 129 to 134 in 37e2e7e

	_deactivate(element, relatedElem) {
	if (!element) {
	return
	}
	element.classList.remove(CLASS_NAME_ACTIVE)

[GeoSot]

I 've checked it and you are right. Thanks, @cpsievert 👍