Rework jspecify tests

1) Add Java use sites which are similar to Kotlin use sites;
2) Use the new test format: separated Java and Kotlin sources (Java declarations + use sites and Kotlin corresponding use sites), Java declarations + use sites will be a sharable test suite;
3) Remove any dependencies from Java sources except `Object` and jspecify annotations;
4) Introduce a new test runner which compiles Java and Kotlin sources together and dumps all descriptors.

compiler/testData/foreignAnnotationsJava8/tests/jspecify/java/testDefaults/DefaultsB.java

@@ -0,0 +1,13 @@
+public class DefaultsB {
+    static void main(DefaultsA a) {
+        a.everythingNotNullable(null).foo();
+        a.everythingNotNullable(new DefaultsA.Test()).foo();
+
+        a.explicitlyNullnessUnspecified(new DefaultsA.Test()).foo();
+        a.explicitlyNullnessUnspecified(null).foo();
+
+        a.defaultField.foo();
+
+        a.field.foo();
+    }
+}