Use the last sample of the PSS/RSS in ApplicationExitInfo

And also fix the issue that the ApplicationExitInfo could be
cleared during package update.

Bug: 148087795
Test: atest ApplicationExitInfoTest
Test: atest CtsAppExitTestCases:ActivityManagerAppExitInfoTest
Change-Id: I79787f3c11b0862bf6a2011eb00cdff96d9a51f7