[FIR] Fix collecting member candidates on receiver with smartcast

^KT-51460 Fixed
^KT-51827

compiler/testData/codegen/box/smartCasts/toStringOnReceiverWIthSmartcast.kt

@@ -0,0 +1,29 @@
+// TARGET_BACKEND: JVM_IR
+// FILE: A.java
+public class A {
+    @Override
+    public String toString() {
+        return "O";
+    }
+}
+
+// FILE: B.java
+public class B {
+    @Override
+    public String toString() {
+        return "K";
+    }
+}
+
+// FILE: main.kt
+fun test(x: Any): String {
+    return when (x) {
+        is A -> x.toString()
+        is B -> x.toString()
+        else -> "fail"
+    }
+}
+
+fun box(): String {
+    return test(A()) + test(B())
+}