Stop adding FLAG_ACTIVITY_RESET_TASK_IF_NEEDED when...

starting a shortcut.

- Also add API surface to support launching multiple intents

- Also add SM.isRateLimitingActive() which was supposed to be
added but was not due to a bad rebase.

Bug 30218829

Change-Id: I82d60ec0df1e2b889538705f9f8870ee727dd55d