fdo#75489 Pass toolbar context menu commands to toolbar for handling.

The toolbar context menu is handled by the toolbar manager, however
the items are provided and managed by the toolbar itself -- previously
any events on the list of toolbar items in the context menu were silently
discarded, whereas now we pass them on to the owning toolbar.

Change-Id: Ia17718c3ff8acfba1b6d655022dd9469932f3493
Toolbar overflow/context menu: keep ordering and don't discard separator.

Previously the overflow/context menu should have had a separator shown
between the overflow items and the hidden items, however these were
inadvertently removed by ImplClearPopupMenu which filters the items
before the menu is displayed.

The previous ordering of items was also the REVERSE of the ordering in
the toolbar -- the overflow menu is a logical extension of the toolbar
hence items should be in the same order as they were in the toolbar.

Change-Id: I8444f4814fea64be1d8f8790445ad6aa01532e70