Copy ApplicationInfo#versionCode field

This compatibility change ensures that apps built for pre-P that rely
on reflection to access ApplicationInfo#versionCode don't crash. The
move to long version code introduces a new field and all modifications
of the field are wrapped in a method that ensures both the new and old
fields are set appropriately.

Test: manual - impacted app runs
Change-Id: I5fb37c65b0fb04042dda12479d1e1a76590daa3d
Fixes: 74393568