[breadcrumbs] Small breadcrumb components refactoring
* use `open_breadcrumbs` and `close_breadcrumbs` methods where applicable in
the BreadCrumbEntityVComponent hierarchy
* include the first separator related code in `open_breadcrumbs` to avoid code
duplication
Closes #3223911.
#!/usr/bin/env python
from cubicweb.cwctl import run
import sys
run(sys.argv[1:])