android-interop-testing: add AndroidX Test core and rules to androidTestImplementation

[shivaspeaks]

This change explicitly adds 'libraries.androidx.test.rules' and 'libraries.androidx.test.core' to the 'androidTestImplementation' configuration.

This alignment follows the pattern used in the 'binder' module to ensure that these testing components are correctly packaged in the Test APK. Previously, these dependencies were only declared in the 'implementation' block (Main APK), which triggered a "classpath split" issue. In that state, the test process was unable to resolve internal orchestration classes, leading to NoClassDefFoundError crashes.

Fixes #12703 (comment)

[ejona86]

Please test this by running the tests using gcloud firebase. Refer to the CI:

grpc-java/buildscripts/kokoro/android-interop.sh

Lines 31 to 43 in 91e9491

	gcloud firebase test android run \
	--type instrumentation \
	--app android-interop-testing/build/outputs/apk/debug/grpc-android-interop-testing-debug.apk \
	--test android-interop-testing/build/outputs/apk/androidTest/debug/grpc-android-interop-testing-debug-androidTest.apk \
	--environment-variables \
	server_host=grpc-test.sandbox.googleapis.com,server_port=443,test_case=all \
	--device model=MediumPhone.arm,version=30,locale=en,orientation=portrait \
	--device model=MediumPhone.arm,version=29,locale=en,orientation=portrait \
	--device model=MediumPhone.arm,version=28,locale=en,orientation=portrait \
	--device model=MediumPhone.arm,version=27,locale=en,orientation=portrait \
	--device model=MediumPhone.arm,version=26,locale=en,orientation=portrait \
	--device model=Nexus6P,version=25,locale=en,orientation=portrait \
	--device model=Nexus6P,version=24,locale=en,orientation=portrait \

[ejona86]

which triggered a "classpath split" issue.

Are you sure? You're telling me that implementation is not part of androidTestImplementation deps? That seems unlikely.

What seems more likely is there's a version skew problem.