Refactor #30544: Deprecate the mount_react_component method
replace mount_react_component with react_component in mount_breadcrumbs
Fixes #30942 - use react_component to mount breadcrumbs
Replaces the deprecated mount_react_component with react_component.
Removes the title, that was replaced by react-dom by the old mechanism, but
now it would duplicate the page title.
Move integration tests, that test breadcrumbs to tests with JS support.
We have been testing dead (invisible with React) elements, so that make no sense.