Group broadcasts occurred within a certain duration into sessions.

For the purposes of tracking whether there is a response event
from an app after receiving a broadcast, treat all broadcasts
received by the app immediately after each other into a single
session and when there is a response event, then treat as if
the app received only one broadcast and there is one response
event corresponding to that.

Bug: 206518114
Test: atest tests/tests/app.usage/src/android/app/usage/cts/UsageStatsTest.java
Change-Id: I4c495d07026a4d6ab445ce463bd1b07e9a89bd06