FIR DFA: add tests about smartcasts in/after try-catch-finally

compiler/testData/diagnostics/tests/smartCasts/castchecks/castInTryWithoutCatch.kt

@@ -0,0 +1,17 @@
+fun castInTry(s: Any) {
+    try {
+        s as String // Potential cast exception
+    } finally {
+        s.<!UNRESOLVED_REFERENCE!>length<!> // Shouldn't be resolved
+    }
+    s.<!UNRESOLVED_REFERENCE!>length<!> // Shouldn't be resolved
+}
+
+fun castInTryAndFinally(s: Any) {
+    try {
+        s as String // Potential cast exception
+    } finally {
+        s as String // Potential cast exception
+    }
+    <!DEBUG_INFO_SMARTCAST!>s<!>.length // Should be smartcast
+}