Shortcut integration with AppSearch (Part 3)

In order to move shortcuts from memory into AppSearch, any in-memory
mutation needs to be identified so that they can be applied directly
into AppSearch. This CL creates a proxy method that applies mutation on
the in-memory copy, which can later be changed to post the update into
AppSearch.

Bug: 151359749
Test: atest ShortcutManagerTest1 ShortcutManagerTest2 ShortcutManagerTest3 ShortcutManagerTest4 ShortcutManagerTest5 ShortcutManagerTest6 ShortcutManagerTest7 ShortcutManagerTest8 ShortcutManagerTest9 ShortcutManagerTest10 ShortcutManagerTest11
Change-Id: I59daa9cc589b587d022a1e070986e07ed6ab0a75