Use correct toString method in IrCompileTimeChecker for analysis

compiler/testData/ir/loweredIr/interpreter/useCorrectToString.kt

@@ -0,0 +1,13 @@
+// This test is needed to check that IrCompileTimeChecker will not fail trying to find and analyze correct toString method
+
+object Obj {
+    override fun toString(): String = "OK"
+
+    fun Int.toString(): String = "Not OK"
+}
+
+const val a = 1 // this is a dummy const to avoid check in IrInterpreterDumpHandler
+
+fun box(): String {
+    return "" + "$Obj" // force a call
+}