Code Lens are a bit of a hidden feature right now, as they are disabled by default. To enable them, add the following to your settings:
Alternatively, you can use the Haxe: Toggle Code Lens command for this.
Once enabled, Code Lens tells you how often a particular field or type is referenced, similar to Find All References.
Code Lens are not just a fancier "Find All References" however. They also include the following information:
subclasses of classes
overrides of methods
implementers of interfaces
subinterfaces of interfaces