Build FrameworkTestRunnerTest with the implementation lib.

FrameworkTestRunnerTests is the test for android.test.runner. The test
accesses various private APIs from the sdk library. Previously, that was
possible because depending on a java_sdk_library gave the implementation
lib of the java_sdk_library for linking. That will be changed after
I14cf217f21fd3534c920c3a6336cf2d14c02e60c where the stubs are by default
provided for linking.

Since this test actually uses some hidden APIs, work around the
restriction by explicitly depending on the impl library.

Bug: 157007292
Test: m FrameworkTestRunnerTests
Change-Id: I0792e9eb1c7c594a1609eb89b6694c1578c86e18