Adds unit tests for ShortcutChangeCallback APIs

Also fixes small bugs and TODOs here and there for tests to pass.

Bug: 153266100
Bug: 153107300
Bug: 148560657
Bug: 148615405
Test: atest com.android.server.pm.ShortcutManagerTest1
            com.android.server.pm.ShortcutManagerTest2
            com.android.server.pm.ShortcutManagerTest3
            com.android.server.pm.ShortcutManagerTest4
            com.android.server.pm.ShortcutManagerTest5
            com.android.server.pm.ShortcutManagerTest6
            com.android.server.pm.ShortcutManagerTest7
            com.android.server.pm.ShortcutManagerTest8
            com.android.server.pm.ShortcutManagerTest9
            com.android.server.pm.ShortcutManagerTest10
            com.android.server.pm.ShortcutManagerTest11
Change-Id: I702de148059296af0a5db70e1a11e4620588a00a