Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/reflection/javaStaticField.kt

@@ -0,0 +1,22 @@
+// FILE: J.java
+
+public class J {
+    static String x;
+}
+
+// FILE: K.kt
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    val f = J::x
+    assertEquals("x", f.name)
+
+    assertEquals(f, J::class.members.single { it.name == "x" })
+
+    f.set("OK")
+    assertEquals("OK", J.x)
+    assertEquals("OK", f.getter())
+
+    return f.get()
+}