DisplayBlock: replace layout with wider margin

Remove a layout and instead use a wider margin around blocks. This is
made easier by the introduction of ViewOutline earlier. It also reduces
flicker considerably when switching the active display block in the
prototype implementation b/409354332.

The display_block_padding value has a different meaning after this
patch. Before it included the highlight width. Now it does not include
the highlight width, so to get the old display_block_padding value two
other values need to be summed up: highlight_width and block_padding

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: visual inspection
Bug: b/409354332
Change-Id: I5a6c8cdd12c9b578425f22d360b8a1c49dfa39f1