Re-enable focus highlight on root list.

Regression was due to the fact we started using a transparent list
selector after switching to manually triggering ripples ourselves.
Without an opaque selector, list view now no longer displays any visual
focus when an item is focused. Using a custom selector that's only for
focus fixes this.

Bug: 30783220
Change-Id: I538110f7a7c0857e2c422867bfb7bbcbe381685d