Enable dagger fastInit on SystemUI

This change enables fastInit mode on SystemUI, which should improve
initialization times.

SystemUIBootTiming was measured over three trials:
- 0ms -> 5ms (DependencyInjection)
- 545ms -> 490ms (StartServices)

Bug: 202327225
Test: - Build and check that sysui uses SwitchingProviders.
      - atest SystemUITests
Change-Id: I726bb1b39af1e26af55b89f7eff80741a31b8ca1