Support two active sdks in EffectiveVersionString

Currently it would return the default one even if the requested one is
an active sdk.

Bug: 270609292
Test: go test ./java
Test: built `rkpdapp` locally in internal and verified that its
targetSdkVersion is U and V
Test: TH

Change-Id: Idb03ff4786ff87fb7911bf31205941618a662404