Extend PackageFreezer for post-commit steps

To ensure that a package is not running during RollbackManager userdata
backup/restore (which could lead to non-deterministic results), the
period for which a package is frozen by PackageFreezer should be
extended
to cover the post-install steps which perform the backup/restore.

In the case of BackupManager restore, the package should be unfrozen
before this takes place. Otherwise, it will be unfrozen on receipt of
the POST_INSTALL message.

Bug: 124032231
Test: atest StagedInstallTest
Test: atest StagedRollbackTest
Change-Id: Ib8eb9b7ceaa86c52bf4bc9d7f3cba53469514cb6