Show appwarnings only if developer mode is on

- Adding check to show appwarnings when developer mode is on
- Adding check to run alignment scan only if new package is being
  scanned

Test: m PageSizeCompatWarningsTest && atest -c PageSizeCompatWarningsTest
Bug: 416538966
Flag: android.content.pm.app_compat_warnings_16kb
Change-Id: I5c209711cb9e6249329a834caf3eb452a33e4216