Dartify all the C++ styled code

[spydon]

The code is written in a very C++ way, this is the first iteration of making it more according to the dart style guide.

Since nobody seems to maintain this repository we have a maintained refactored version over here:
https://github.com/flame-engine/forge2d

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[spydon]

@googlebot I signed it!

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