sp-api: Use `EncodeAs` for parameters

[bkchr]

We should use EncodeAs for the parameters passed to a generated trait function. This should make it easier from the node side to call these runtime functions as in the end everything that encodes to the same type can be passed. Internally the parameters are forwarded using SCALE any way.

[dharjeezy]

Hello @bkchr does this mean we will inject the EncodeAs constraint into parameter types in the trait function signature which should be done in this function generate_runtime_decls?

[bkchr]

Yeah that was my rough idea, but maybe it doesn't work.

[dharjeezy]

Oh. I am quite curious why you think that may not work? and also do you have another proposition on how it can be implemented? @bkchr

[bkchr]

Just try if it works and then we will know :)