Introducing teleportation between sections.

The key combos differ from the ones in the spec because key combos
including Meta key don’t get delivered to apps. To fix this, I’ll
implement necessary plumbing after the feature freeze. Meanwhile,
temporary combos are used.

Given that the section and cluster teleportation have a lot in common,
I’m not introducing new methods, but adding a param to the cluster
teleportation ones. I should have also changed the names to something
like findNextKeyboardNavigationCluster => findNextFocusGroup, where
“FocusGroup” is a generalized name for clusters and sections.
However, that name depends on b/33708251, so I’m not doing it now. I
don’t rename existing identifiers, and using “focusGroup” for new
ones. Admittedly, this creates mess that will be resolved based on
the outcome of the mentioned bug.

Bug: 32151632
Test: Manual checks; CTS are coming after feature freeze
Change-Id: I01b5d6e5a9689b8f643fa4af695d2ce61265f374