[FIR] Fix collecting member candidates on receiver with smartcast

^KT-51460 Fixed
^KT-51827

compiler/testData/diagnostics/tests/smartCasts/kt51460.kt

@@ -0,0 +1,18 @@
+// FIR_IDENTICAL
+// ISSUE: KT-51460
+
+abstract class A {
+    abstract protected val a: A?
+
+    class B(override val a: A?) : A() {
+        fun f(other: A) {
+            val x = if (other is C) {
+                other.a
+            } else {
+                null
+            }
+        }
+    }
+
+    class C(override val a: A?): A()
+}

compiler/testData/diagnostics/tests/smartCasts/kt51460.txt

@@ -0,0 +1,26 @@
+package
+
+public abstract class A {
+    public constructor A()
+    protected abstract val a: A?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public final class B : A {
+        public constructor B(/*0*/ a: A?)
+        protected open override /*1*/ val a: A?
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final fun f(/*0*/ other: A): kotlin.Unit
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public final class C : A {
+        public constructor C(/*0*/ a: A?)
+        protected open override /*1*/ val a: A?
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}