Library modernization with @:structInit

[Yanrishatum]

Since Haxe 3.4 there were implemented new feature for static structures - @:structInit which gives a lot better performance for static targets. Entire library is built around typedef and their performance for static targets is questionable as they based on Dynamic.

Proposal:
Use @:structInit whenever possible instead of typedefs or at least use them for targets where it would improve performance.

Pros:

• Better performance on static targets.

Cons:

• Most probably worse performance on dynamic targets.
• Requires a lot of work to update.
• Produces #if (haxever >= 3.4) and/or target checks everywhere.

Personal interest:
I extensively use my tmx format-like library and it's structure based on typedefs as well, but as we use C++ target, I do not like the overall performance during file processing, as I need it working as fast as possible because they need to be loaded realtime during gameplay. I wanted to rework library and do a pull request with it, but I do not like using typedefs for static targets.

[ncannasse]

I think it would only work for typedefs that might been use a lot in the file format or which have a lot of fields accesses. If it's for the top level typedef's ("Data" type) that doesn't make much a difference.

I'll close the issue for now, please submit a PR if you wish to change some actual specific typedef by adding @:structInit