Minor, move tests about Java field and Kotlin property

Because the `fieldRename` directory was originally about cases when
private fields are renamed because of clashes.

compiler/testData/codegen/box/javaFieldAndKotlinProperty/javaFieldAndKotlinPrivateProperty.kt

@@ -0,0 +1,18 @@
+// TARGET_BACKEND: JVM_IR
+// Note: works accidentally via backing field access
+// Field VS property: case 4.2
+// More or less duplicates the case in KT-34943/KT-54393
+
+// FILE: BaseJava.java
+public class BaseJava {
+    public String a = "FAIL";
+}
+
+// FILE: Derived.kt
+class Derived : BaseJava() {
+    private val a = "OK"
+
+    fun x() = a
+}
+
+fun box() = Derived().x()