Badging should print package attributes at most once

Following up to change 7938786; if an APK had platformBuildVersionCode
compiled as *both* integer and string, it would be output twice. This
then confuses anything that tries to parse the output.

With this change, the value will be printed at most once, with the
string version taking priority.

Bug: 138666693
Test: manually built SDK28 APK and ran aapt2 dump badging
Change-Id: Icf6eb656ac0cb263969bb2f0c5ca03139985f6ca