FIR: fork flow on function entry, restore receivers on exit

^KT-52680 Fixed

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

@@ -0,0 +1,24 @@
+interface I {
+    val prop: Int
+}
+
+open class A {
+    fun f1() {
+        this as I
+        <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>prop<!>
+    }
+
+    fun f2() {
+        <!UNRESOLVED_REFERENCE!>prop<!>
+    }
+}
+
+open class B {
+    fun f() {
+        {
+            this as I
+            <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>prop<!>
+        }
+        <!UNRESOLVED_REFERENCE!>prop<!>
+    }
+}