Allow passing a cause to predefined error functions

[Mrtenz]

This allows passing an Error class object to one of the predefined error functions as defined in rpcErrors and providerErrors. Upon calling the serialise function of the JsonRpcError class, the cause error will be serialised using the serializeCause function.

For example:

consterror=rpcErrors.invalidParams({data: {cause: newError('foo bar'),},});

Callng error.serialize() results in:

{
"code": -32602,
"message": "Invalid method parameter(s).",
"data": {
"cause": {
"stack": "Error: foo bar [...]",
"message": "foo bar"
}
},
"stack": "Error: Invalid method parameter(s). [...]"
}