One rendered overflow row: the free headerOverflow tab renderer wrapped with
activate-on-click, built by core and reused by the advanced overflow list so
the row DOM + behaviour stay identical to the free dropdown.
Expand the panel's tab group if collapsed, activate the panel (origin
'user') and close the popover, identical to clicking the row. Used by
the keyboard controller (Enter).
One rendered overflow row: the free
headerOverflowtab renderer wrapped with activate-on-click, built by core and reused by the advanced overflow list so the row DOM + behaviour stay identical to the free dropdown.