Add ARIA `role` attribute to components where applicable

All existing components need ARIA roles assigned. This is needed for screen reader devices, etc. to know what a plain <div> semantically refers to. Note that most of the time we don't use semantic elements like <button>, because it's not allowed to attach shadow DOM to such elements. As an example, ToolButton which currently renders (give or take) as <div class="bk-ToolButton">, would become <div class="bk-ToolButton" role="button">.