Fix PackageManager query API's related to rebootless APEX updates

There were two bugs:

1. In case of the first update, ApexManager removed information about
  pre-installed version of the APEX.
2. After an update, getPackageInfo cache wasn't invalidated, which
  resulted in getPackageInfo returning stale information.

Bug: 193085724
Test: atest ApexManagerTest
Test: atest StagedInstallInternalTest
Change-Id: I6df7b296cd5d83c93524178f1546855747ea6b07