Prevend user spoofing in isRequestPinItemSupported

This CL ensure the caller process is from the same user when calling
ShortcutService#isRequestPinItemSupported.

Bug: 191772737
Test: atest ShortcutManagerTest1 ShortcutManagerTest2
    ShortcutManagerTest3 ShortcutManagerTest4 ShortcutManagerTest5
    ShortcutManagerTest6 ShortcutManagerTest7 ShortcutManagerTest8
    ShortcutManagerTest9 ShortcutManagerTest10 ShortcutManagerTest11
    ShortcutManagerTest12
Test: atest CtsShortcutManagerTestCases
Change-Id: Icab7cdf25b870b88ecfde9b99e107bbeda0eb485