Teleportation between clusters.

Per the UX spec, key combos for quickly jumping between clusters are
Meta+Right and Meta+Left. However, these events don’t get delivered
to the app, and I’ll have to implement this plumbing after the
feature freeze. For now, the temporary combos are Ctrl-Shift-”-”
and Ctrl-Shift-”+”.

In addition to the key combo processing, the CL adds public APIs for
teleportation; they are similar to the API for moving the focus.

Bug: 32151632
Test: Manually checking that teleportation works. CTS test will be
added after the feature freeze.

Change-Id: I622156b9e4cc7c44e61623081d6d079bbe04fd02