Draft: parse_androidmanifests: order by max_vercode

This reverts 83ffeb85, which shortcutted the detection code to always prefer build.gradle. The workaround was done by ending the paths loop early and using the found versions directly. This makes the function hard to extend with other file formats, for example pubspec.yaml as gradle would take precedence.

Instead the new code strictly uses the highest version information based on the assumption that an app can change the build system build not lower the version code.

There is one related bug we need to fix. The old max_vercode computation below the paths loop, i.e.: and (max_vercode is None or vercode > max_vercode):, uses '>' to compare the version code but vercode and max_vercode are strings, resulting in a bogus string compare. This has been fixed by converting vercode to int and only converting it back to string before returning the function result. This entailed fixing one unit test.