New J2K: fix assignment target in ConvertGettersAndSettersToPropertyProcessing

#KT-36190 fixed

nj2k/testData/newJ2k/detectProperties/IsPrefixSetterCall.java

@@ -0,0 +1,10 @@
+public class TestSetter {
+    private static void setThing(int thing) { }
+
+    private static int isThing() { return 42; }
+
+    public static void main(String[] args) {
+        setThing(42);
+        System.out.println(isThing());
+    }
+}

nj2k/testData/newJ2k/detectProperties/IsPrefixSetterCall.kt

@@ -0,0 +1,11 @@
+object TestSetter {
+    private var isThing: Int
+        private get() = 42
+        private set(thing) {}
+
+    @JvmStatic
+    fun main(args: Array<String>) {
+        isThing = 42
+        println(isThing)
+    }
+}