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/Simple.java

@@ -0,0 +1,22 @@
+import org.jspecify.annotations.*;
+
+public class Simple {
+    public static class Base {}
+    public static class Derived extends Base {
+        void foo() {}
+    }
+
+    @Nullable public Simple.Derived field = null;
+
+    @Nullable
+    public Simple.Derived foo(Derived x, @NullnessUnspecified Base y) {
+        return null;
+    }
+
+    static public void main(Simple a) {
+        a.foo(new Derived(), null).foo();
+        a.foo(null, new Derived()).foo();
+
+        a.field.foo();
+    }
+}