505: Inherent methods r=matklad a=flodiebold
This adds resolution, type checking and completion for inherent methods.
The main open question here is the caching, I think. I'm not sure whether we should be caching method resolutions in a more fine grained way (currently we just build a hash map of types -> impl blocks, and iterate through all potential impl blocks when looking for a method).
Co-authored-by: Florian Diebold <flodiebold@gmail.com>
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