Only allow low target sdk bypass when system, root or shell

If the --bypass-low-target-sdk-block flag is passed in to
package manager, ignore the flag if the calling UID is not
system, root, or shell (except when on debuggable builds).

Bug: 237321649
Test: run cts
Change-Id: I90d23658b13a24be6974bdf74e59d887b3adc3ab