Pass config changes through to TaskbarDelegate

* Previously TaskbarDelegate was listening for config
changes, but there was a race condition between when
it was initialized and when the config change
callback happened. The callback didn't re-fire after
TaskbarDelegate became a listener for it.
* Rely on NavigationBarController, whose lifecycle
outlives TaskbarDelegate, to pass through config
changes to TaskbarDelegate (similar to how it's doing
for NavigationBar today)

* One caveat is that previously TaskbarDelegate was
relying on WM.ComponentCallbacks#onConfigChanged()
whereas NavigationBarController gets its config
changes from Application#onConfigurationChanged()

Fixes: 243765256
Test: Repro in bug no longer happens
Change-Id: Ifa7ea26946e6e68f74d095cbdf1e274d6a39b6b7