[Status Bar Refactor] 2.2/N: Migrate StatusBar's panelExpansionChanged

callback to the correct listener interface.

StatusBar also had two different methods called when
panelExpansionChanged happened, so those methods are merged into one.

Test: manual (verified callback still triggers correctly)
Test: atest SystemUITests
Bug: 200063118
Change-Id: I90011b0e0bb9bb57accf82806cef7d5c44e19a7f