[pm] move Computer related classes to separate files

+ Moved DomainVerificationConnection
+ Added MovePackageHelper
+ Moved a few static methods to PackageManagerServiceUtils

BYPASS_INCLUSIVE_LANGUAGE_REASON=simply moving code around

BUG: 196253436
Test: manual
Change-Id: I347303c019d7b6c69dd8ac03b19ae89a4d688df6