Add single interface for SysUI to call into Shell

- Currently update configuration callbacks to use this interface
  so that individual features don't need to expose their own config
  change callbacks.  Will followup with moving keyguard/shell init
  /shell command handler.

Bug: 238217847
Test: atest WMShellUnitTests

Change-Id: Id526ed588de8cf962e821a3b9e1933a67f354d77