Adds CACHED shortcuts and methods to retrieve and remove

Adds a new flag to ShortcutInfo to mark it as cached. Also adds new
APIs in ShortcutManager to remove or retrieve a cached shortcut.

Bug: 148084870
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
Change-Id: I859b416ccd4228eec10a436550ff98866a62af66