[pm] retain old code paths for INSTALL_DONT_KILL_APP

Previously, for split installs with DONT_KILL, the deletion of old code
paths are delayed for 3 seconds. This CL further delays it for a day or
the next reboot.

The change is guarded by a feature flag.

Test: manual with the following steps
1. adb shell device_config put package_manager_service
   android.content.pm.improve_install_dont_kill true
2. adb reboot (system server will pick up the new flag value on reboot)
3. test split installs with --dont_kill and verify that the old dirs are
   preserved until next reboot

Test: atest with the previous steps to enable the feature flag
atest
cts/tests/tests/content/src/android/content/pm/cts/InstallDontKillTest.java

BUG: 291212866

Change-Id: I49c328c0d9f55c87b18b8c1aeecdc62659b58364