DisplayTopology: fix erroneous attach-to-corner

Using x/y deviation to choose which edge to attach to was causing corner
attachment too easily when only a small amount of the larger edge was
overlapping. Effectively the block would be bumped to the corner even
though attaching along the longer edge would have been closer to the
requested position.

Do not use deviation to choose an attachment edge, but use the overlap
values. Update comments accordingly, as well as reword and refactor
them.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: atest DisplayTopologyTest.kt
Bug: b/352650922
Change-Id: I38024ab1500020fe195348e96b0c99ec85886e03