Low battery notifications for USI styluses.

USI stylus low battery notifications should only appear when
bluetooth battery notifications are not available.

There is currently no way to differentiate USI styluses, so any
USI stylus being used will use the same notification.

Bug: 250908244
Test: StylusUsiPowerStartableTest StylusUsiPowerUiTest
Change-Id: I54cb59c1608c955f19db4776875e0dc3d9df1dd5