[sdks/android] Workaround Android Studio JUnit test runner runtime classpath issue.

sdks/android/Mentat/library/build.gradle

@@ -68,11 +68,30 @@ cargo {
     defaultToolchainBuildPrefixDir = Platform.RESOURCE_PREFIX
 }
 
+configurations {
+    // There's an interaction between Gradle's resolution of dependencies with different types
+    // (@jar, @aar) for `implementation` and `testImplementation` and with Android Studio's built-in
+    // JUnit test runner.  The runtime classpath in the built-in JUnit test runner gets the
+    // dependency from the `implementation`, which is type @aar, and therefore the JNA dependency
+    // doesn't provide the JNI dispatch libraries in the correct Java resource directories.  I think
+    // what's happening is that @aar type in `implementation` resolves to the @jar type in
+    // `testImplementation`, and that it wins the dependency resolution battle.
+    //
+    // A workaround is to add a new configuration which depends on the @jar type and to reference
+    // the underlying JAR file directly in `testImplementation`.  This JAR file doesn't resolve to
+    // the @aar type in `implementation`.  This works when invoked via `gradle`, but also sets the
+    // correct runtime classpath when invoked with Android Studio's built-in JUnit test runner.
+    // Success!
+    jnaForTest
+}
+
 dependencies {
+    jnaForTest 'net.java.dev.jna:jna:4.5.2@jar'
+
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
     implementation 'net.java.dev.jna:jna:4.5.2@aar'
 
-    testImplementation 'net.java.dev.jna:jna:4.5.2'
+    testImplementation files(configurations.jnaForTest.files)
     testImplementation 'junit:junit:4.12'
     testImplementation 'org.robolectric:robolectric:3.8'
     testImplementation 'org.mockito:mockito-core:2.20.0'