Created by: pvdlg
Fixes #21691 (closed), fixes #21706 (closed)
Currently the navbar-toggleable-* breaks at viewport size of the next breakpoints (i.e navbar-toggleable-md breaks at 992px instead of 768px).
This PR fix the navbar-toggleable-* generation to break at the corresponding breakpoint.
In addition, it generate navbar-toggleable that would prevent the navbar to collapse at all viewport size and mention it in the docs.
Finally it mentions in the docs that a navbar without navbar-toggleable-* will make it always collapsed.
It might be useful in order to created always/never collapsed navbar (as requested in #21706 (closed))