Update hotseat alpha in TaskbarLauncherStateController#init()

Technically the consumer should do that already, but the consumer isn't called if the value isn't changed (in this case, it's going from 1 to 1). So explicitly call the consumer once in init().

Test: Open an app, toggle dark theme from quick settings, go home and ensure hotseat isn't visible during the transition
Fixes: 211002647
Change-Id: I5a9680282b3982d9b6f982833cd671b224767518