Support AARs through qt_add_library()

Android AARs are meant to be libraries, however, atm they're treatable more like executable apps with androiddeployqt for some reason.

Under this work, we should aim to properly support building AARs mainly under qt_add_library() instead of qt_add_executable().

Since both this mentioned above and building and managing Jar dependencies go through Gradle eventually, we could support building Qt Jars using qt_add_library() as well (see QTBUG-85232).