Replaced RegExp method parser with recursive descent

Summary:
public

This diff replaces the RegEx module method parser with a handwritten recursive descent parser that's faster and easier to maintain.

The new parser is ~8 times faster when tested on the UIManager.managerChildren() method, and uses ~1/10 as much RAM.

The new parser also supports lightweight generics, and is more tolerant of white space.

(This means that you now can – and should – use types like `NSArray<NSString *> *` for your exported properties and method arguments, instead of `NSStringArray`).

Reviewed By: jspahrsummers

Differential Revision: D2736636

fb-gh-sync-id: f6a11431935fa8acc8ac36f3471032ec9a1c8490

React/Base/RCTNullability.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <Foundation/Foundation.h>
+
+typedef NS_ENUM(NSUInteger, RCTNullability) {
+  RCTNullabilityUnspecified,
+  RCTNullable,
+  RCTNonnullable,
+};