Implement the Wasm wide-arithmetic proposal

[Robbepop]

This is about adding support for the wide-arithmetic Wasm proposal.

The wide-arithmetic Wasm proposal has just been moved to implementation phase 3 of the standardization process. Thus major changes are no longer to be expected. Therefore it now makes sense to implement this Wasm proposal in Wasmi.

Having support for wide-arithmetic would improve performance even for interpreter runtimes such as Wasmi for certain use cases. The proposal is very small and thus not a lot of work and therefore can be implemented easily or quickly.