Whenever something changed on the selected element (pseudo, attribute), the
breadcrumbs widget used to loop over all breadcrumbs buttons and re-create the
markup for each.
Now, we cache a string version of the text displayed in a button and compare
the new value to that in the loop, to skip DOM updates.
Additionally, the breadcrumbs widget used to update itself after all markup mutations
in the DOM tree displayed in the inspector. The update method now looks at the mutations
array and early return if none of them actually impact the displayed breadcrumbs.
