FlxAtlasFrames.fromTexturePackerJson(): allow passing a parsed description

[MSGhero]

Closes #2019

In case the JSON is already parsed to an object, this avoids hundreds of thousands of allocations for big spritesheets.

[Gama11]

Hm.. I guess there isn't really a way to avoid Dynamic here?

A unit test would be nice. IIRC, we already have some for fromTexturePackerJson().

[Gama11]

I wonder whether it'd make sense to use OneOfTwo<String, Dynamic> here. Of course it doesn't add any type safety, but it might serve as self-documentation in a way.

[MSGhero]

I guess the most type-safe way to handle the dynamic is to expect the frames property. Could also be a private typedef TPObject if this looks gross.

OneOfTwo<String, { frames : Array<Dynamic> }>

[Gama11]

Is it really guruanteed to be an array? There's some code for "JSON-Hash".

[MSGhero]

Oh dang, I meant frames : Dynamic which is better than nothing. It would prevent you from putting 5 there, at least.

[Gama11]

Yeah, that seems sensible.

[MSGhero]

👍 I think, I haven't run unit tests locally in a while.