Disable mirror toggle if feature turned off

If the content mode management feature is disabled, the mirror display
toggle should be disabled, and instead reflect the inverse of the
"force desktop on external displays" system property.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: manual with and without toggle user-changeable
Bug: b/396116157
Change-Id: I550fc918aaebab7129a559c0e49b88c8da7bc00d