Add more tests

Author: HassanElDesouky

test/Constraints/optional.swift

@@ -438,6 +438,7 @@ func sr_12309() {
   _ = nil! // expected-error {{'nil' literal cannot be force unwrapped}}
   _ = (nil!) // expected-error {{'nil' literal cannot be force unwrapped}}
   _ = (nil)! // expected-error {{'nil' literal cannot be force unwrapped}}
+  _ = ((nil))! // expected-error {{'nil' literal cannot be force unwrapped}}
   _ = nil? // expected-error {{value of optional type 'Optional<_>' must be unwrapped to a value of type '_'}}
            // expected-note@-1 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
            // expected-note@-2 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}