[pm] allow debuggable apps to be downgraded on release builds

By preserving the INSTALL_REQUEST_DOWNGRADE flag throughout the
installation session, we can check whether the app is debuggable and
downgradable at a later stage of the installation during
isDowngradePermitted(). If the app is debuggable and the downgrade has
been requested, the installation should be allowed.

BUG: 272769908
Test: atest CtsPermissionTestCases android.permission.cts.LocationAccessCheckTest#notificationIsNotShownAfterAppDoesNotRequestLocationAnymore
Change-Id: Ic5d9c7b65a70ba343a0bb1c5405537fc37f7ec8c