Limit Blocking Time for TelephonyManager.getModemActivityInfo

-Add new delayed message handler EVENT_BLOCKING_RESPONSE_TIMEOUT
 that will ensure a specific REQUEST sent to RIL is no longer
 pending for a response. If a response is pending, this timeout
 will generate and return a default error response to unblock
 blocking calls. If RIL subsequently returns a response for the
 request, it will be discarded.

-Create a default blocking timeout of 2 seconds

Bug: 28007638
Bug: 26842468
Change-Id: I92e028476522f7604626f3670f2f63e5bb64deec