Add two panel home support for page binding logic

There's a logic which prioritizes the binding for the
current page and defers the other pages' binding.
If two panel home is enabled, we want to bind both pages
together. LauncherPageRestoreHelper has been created to
contain the logic for persisting restoring and calculating
which pages to load immediately.

Test: manual + run LauncherPageRestoreHelperTest robo test
Bug: 174464691
Change-Id: I57ac3f7150303b95b272e922f44bda26f9d5ce2a