HaxeContext: Update keyword list

This updates the keyword list in `Context.cs` directly [based on the keywords defined in the Haxe compiler](https://github.com/HaxeFoundation/haxe/blob/development/ast.ml#L492) (thanks @Simn for pointing me there). I also changed the format to be a bit more readable.

Effectively, this adds `static`, `private`, `public`, `this`, `extern`, `in`, `override`, `package` and `macro` to the list - I'm not sure, is there a reason for them not having been there before? Is FD's definition of a keyword different?

It also removes `type` and `callback`, which are not keywords.

I'm thinking I must have missed something, because `calback` is still highlighted in blue after rebuilding FD (albeit doesn't show up as a template in auto completion anymore) - I assume syntax highlighting elsewhere? If so, shouldn't it use the same list of keywords?