Add keyguard callbacks to ShellInterface

- Currently multiple shell feature interfaces expose the same
  keyguard visibility callback, instead we can pipe this signal
  to the shell for controllers to register for events.

Bug: 238217847
Test: atest WMShellUnitTests
Test: atest SystemUITests
Change-Id: I96125e9f3796c8303683c9314f13884121ded39d