Unify RPC response type

[igor-sirotin]

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Description

We use 3 functions to build an RPC response:

• makeJSONResponse
• prepareJSONResponse
• prepareJSONResponseWithCode

They use 2 different types of responses used.

Because of this we have to parse the response depending on the actual method called.

APIResponse

Definition:

This only allows to return an error: https://github.com/status-im/status-go/blob/91c6949cd25449d5459581a21f2c8b929290ced0/mobile/types.go#L9-L12

I suppose that's why we have some custom response types: https://github.com/status-im/status-go/blob/91c6949cd25449d5459581a21f2c8b929290ced0/mobile/types.go#L14-L25

jsonrpcErrorResponse and jsonrpcSuccessfulResponse

These look more universal. It allows to return an error (with a code defined) or data.

Definition:

https://github.com/status-im/status-go/blob/c0c963bdaade096dd0ce6eb7b9eed9ef7620f652/mobile/response.go#L28-L39

Problem

The main interesting field in these responses is error. And it's defined at different levels (response.Error vs response.Error.Message), so I have to know what to expect from particular endpoint.

[igor-sirotin]

cc @cammellos

[AryanGodara]

@igor-sirotin @cammellos Hi, I would really like to work on this issue (: I see that it hasn't been taken up yet, so is it okay if I start working on this one?