Initialize lastUsedElapsedTime to Integer.MIN_VALUE.

Since 'lastUsedElapsedTime' indicates the timestamp at which
the app was last used by the user and this isn't necessarily
the reason why we create AppUsageHistory objects, we shouldn't
be initializing the 'lastUsedElapsedTime' to the timestamp at
which the object is being created.

Also, update 'lastPredictedTime' to Integer.MIN_VALUE as
getElapsedTime() time doesn't return predictable values for
timestamps in the past and passing getElapsedTime(0) isn't
accurate as it basically indicates the timestamp at boot.

Bug: 206518483
Test: atest tests/tests/app.usage/src/android/app/usage/cts/UsageStatsTest.java
Change-Id: Ib90b435b1efc34144f0461aaaf339fc6037ecdc2