pm: SharedUserId: Assign seinfo using actual targetSdkVersion

Assign the targetSdkVersion component of SeInfo using the lowest
targetSdkVersion of all apps within a SharedUserId.

Bug: 72290969
Test: cts-tradefed run cts -m CtsAppSecurityHostTestCases
Test: cts-tradefed run cts -m CtsSelinuxTargetSdk{current,25,27}TestCases
Test: install sharedUserId app with targetSdkVersion=28, then install
    app with targetSdkVersion=26. Verify that they share the same domain
    and data is correctly labeled.
Change-Id: I9476d10bf3c6a769d63a45a4314aaa91203880b8