Merge abandon() methods (14/n)

Unify the code flow of abandon() since non-staged sessions now also
have READY/APPLIED/FAILED states.

1. set mStageDirInUse to true to prevent deleting staging files
   when verification is in progress.
2. After verification, process pending abandon() request if any
   and abort the install process.
3. set mStageDirInUse to true again when install phase is about
   to start.

Bug: 210359798
Test: atest CtsRootPackageInstallerHostTestCases \
            CtsAtomicInstallTestCases
Change-Id: I2b2e417ba09304daad5edee03e5717a414d4c023