Apply READY/FAILED to non-staged sessions (12/n)

* Merge PackageSessionVerifier#VerifyNonStaged and
  PackageSessionVerifier#VerifyStaged. Now we have a single entry
  point, PackageSessionVerifier#verify to do verificaiton for both
  staged and non-staged sessions in one call.
* PackageSessionVerifier will change session states (either READY or
  FAILED) when verification is completed.

Bug: 210359798
Test: atest StagingManagerTest \
            CtsAtomicInstallTestCases \
            GtsStagedInstallHostTestCases \
            CtsRootPackageInstallerHostTestCases \
            CtsStagedInstallHostTestCases \
            CtsInstallHostTestCases \
            StagedInstallInternalTest

Change-Id: I8c00b817b86d8287704139b9f0769bb05d53d3c7