AI 146394: Add ExampleAppWidgetConfigure to manifest and correct update issues.

  This adds widget configuration to manifest so we don't crash when trying to insert.  We also correctly push a second update once prefix title has been saved; previously we showed a stale title until next widget update.  Also return the title prefix correctly for a given appWidgetId.
  BUG=1792887

Automated import of CL 146394