Add test case for 'useUnknownInCatchVariables'.

tests/cases/compiler/useUnknownInCatchVariables01.ts

@@ -0,0 +1,23 @@
+// @useUnknownInCatchVariables: true
+
+try {
+    // ...
+}
+catch (e) {
+    // error!
+    void e.toUpperCase();
+    void e++;
+    void e();
+
+    if (typeof e === "string") {
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+    }
+    if (e instanceof Error) {
+        e.stack?.toUpperCase();
+    }
+    if (typeof e === "number") {
+        e++;
+    }
+}