Integrate with snapshot testing

[kvark]

https://github.com/mitsuhiko/insta
Depends on #32

[paulkernfeld]

I just pushed a branch with a prototype of this implementation, but maybe it doesn't make sense to open a PR until #48 is merged.

[kvark]

Ah I see. Yes, let's merge serialization first, then make it nice (the Handle stuff), then proceed with snapshots. And thank you for all the hard work here, it's amazing to see these changes coming ❤️

[pjoe]

One issue: having the handle ids in the snapshots will fail the cases where ordering changes, but module is still semantically identical. Think e.g. a different glsl parser that orders expressions slightly different.

I'm not sure general snapshot testing can handle this. I've previously worked on some similar testing for a glTF exporter, where we ended up de-referencing indexed data before doing comparison between actual and expected results. In this way you 'abstract away' the specific ordering and index values, where they don't have any semantic difference.