FIR2IR: Fix smart-cast approximation implicit receiver

Previously, it was always cast to the first type of smart cast variants list
independently of callee symbol that might be present in the member scope
of a different type

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

@@ -0,0 +1,17 @@
+interface Bound
+interface CompilerPhase<in X1 : Bound, Y1>
+
+private class CompositePhase<X2 : Bound, Y2>(
+    val foo: String
+) : CompilerPhase<X2, Y2>
+
+@Suppress("UNCHECKED_CAST")
+fun <X3 : Bound, Y3> CompilerPhase<X3, Y3>.bar(): String {
+    this as CompilerPhase<X3, Any?>
+    val ok = if (this is CompositePhase<X3, *>) foo + "K" else "fail"
+    return ok
+}
+
+fun box(): String {
+    return CompositePhase<Bound, Int>("O").bar()
+}