Added test for finding subpackages in mixed Java & compiled Kotlin package.

compiler/testData/loadJava/compiledJavaAndKotlin/MixedPackage/JavaClassInSubpackage.java

@@ -0,0 +1,7 @@
+package test.sub;
+
+public class JavaClassInSubpackage {
+    public void instanceMethod() {}
+
+    public static void staticMethod() {}
+}