Make QS listen when expanded over Lockscreen

QS needs to be told to listen for tile state changes whenever shade
expansion state changes. This change adds a call to QS.setListening
when it changes the state of System UI to SHADE_LOCKED.

Fixes: 403434908
Test: Manually reproduced bug and verified fix
Test: added unit test coverage
Flag: EXEMPT tiny bug fix
Change-Id: I4060591dd50d44f30c8f776d1908ff6b9d511611