NbSidebarService onExpand() don't get event when sidebar is expanded by click on nb-menu item with submenu

[przemekpobuta]

Issue type

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• bug report

Issue description

Current behavior:
Example from ngx-admin: NbSidebarComponent is compacted state, when clicked on menu (NbMenuComponent) item (only icon in compacted sidebar state) with nested items, then sidebar expand, but any event from available in NbSidebarService Observables isn't fired.

Expected behavior:
In my opinion method onExpand() from NbSidebarService should emit event after sidebar changed state from e.g. compacted to expanded. Or more appropriate, any way to track sidebar state.

Angular, Nebular

@nebular/theme: 3.4.2
@angular: 7.*.*