[FIR] Support fields as part of graph of class initialization

^KT-49747 Fixed

compiler/fir/analysis-tests/testData/resolve/smartcasts/smartcastInByClause.kt

@@ -0,0 +1,21 @@
+// ISSUE: KT-49747
+// DUMP_CFG
+
+class A(val path: String?, val index: Int)
+
+interface Base
+class Derived(val index: Int) : Base
+
+fun test(a: A?): Base? {
+    val path = a?.path ?: return null
+    takeInt(a.index) // should be ok
+    return object : Base by Derived(a.index) {
+        val x: Int = a.index
+
+        fun foo() {
+            takeInt(a.index)
+        }
+    }
+}
+
+fun takeInt(x: Int) {}