[BottomNavigationView] Request for FAB support similar to BottomAppBar

I have scenario that I would need to add FAB to the BottomNavigationBar similar to this screenshot.


Apparently I see that BottomAppBar have this scenario supported, but not for BottomNavigationBar

**Describe the solution you'd like**

Provide similar FAB support from BottomAppBar to BottomNavigationBar.

**Describe alternatives you've considered**

Here is how I workaround at the moment by readjust my existing layout to achieve the same UI. Suggestions also welcome if it will not fit to include in libs (Probably can be app-specific use case rather to be included in libs I guess?).

**Layout**

**Menu**

Start by reviewing the existing BottomNavigationView and BottomAppBar behavior, with the provided CoordinatorLayout and FloatingActionButton layout as the reference case. Determine whether equivalent FAB support belongs in the component and define the expected navigation and menu behavior; done means the requested BottomAppBar-like integration is supported or its scope is clearly resolved.

Written by the indexing model from the issue text.