publicField -> JvmField

Effectively drop publicField and introduce JvmField (which has the same effect for now)
Implement frontend checks for @JvmField
Replace publicField -> JvmField in test data

compiler/testData/codegen/boxWithJava/jvmField/simple/Test.java

@@ -0,0 +1,6 @@
+public class Test {
+    public static String invokeMethodWithPublicField() {
+        C c = new C();
+        return c.foo;
+    }
+}