Add instrumented app to JAR path (isolated splits)

The base APK is loaded during normal execution even when isolated splits
are requested. This preserves that behavior during instrumented tests,
which previously skipped the base APK (causing class loading errors).

Test: tested on device with a trivial automated instrumented test
Bug: 146183755
Change-Id: Ia54072ee91b7c06cb4a787a8954ad2e69b322cac