Docs: navbar menu buttons, menu JS toggle, delegated tooltips (#42552)

Docs: navbar menu buttons, menu JS toggle, delegated tooltips (#42552)

* Docs: use <button> for navbar menu toggles instead of <a href="#">

A menu toggle is a button, not a link. Replace the navbar dropdown
toggles' `<a href="#" role="button">` with semantic `<button>`
(.nav-link already resets button styling). Fixes #40995.

* Docs: show how to open/close/toggle a menu via the JS API

The Via JavaScript section only showed instantiation. Add an example
using getOrCreateInstance().show()/hide()/toggle(). Fixes #37042.

* Docs: document delegated tooltips via the selector option

Add an example initializing one Tooltip on a parent with the selector
option to cover many (and dynamically-added) triggers. Fixes #41020.