[FIR] Don't save DFA implications for unstable local vars

^KT-57502 Fixed

compiler/testData/diagnostics/tests/smartCasts/variables/localDelegatedProperty.kt

@@ -0,0 +1,13 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+// ISSUE: KT-57502
+
+import kotlin.properties.Delegates
+
+fun test(foo: Any) {
+    var test by Delegates.observable(true) { property, oldValue, newValue ->  }
+    test = foo is String
+    if (test) {
+        foo.<!UNRESOLVED_REFERENCE!>length<!> // no smartcast
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/boundInitializer.fir.kt

@@ -15,6 +15,6 @@ fun foo(arg: Int?) {
     var z = arg
     z = z?.let { 42 }
     if (z != null) {
-        arg.hashCode()
+        arg<!UNSAFE_CALL!>.<!>hashCode()
     }
 }