Show border highlight when dragging display

In the process of adding highlight we use an extra feature of
LayerDrawable to add insets so that we can add padding without changing
the actual dimensions or position of the DisplayBlock Views.

To make it easier to keep the values consistent and to aid in conversion
between px and dp, use dimen values to store padding and highlight
metrics.

Bug: b/352650922
Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: atest DisplayTopologyPreferenceTest.kt
Change-Id: I51ff2ce4a086e84a0c529346f8ede90430090b11