eth/tracers: add ReturnData in the tracer's response (ethereum#27704)

The struct logger (or opcode tracer) was missing the return data field even
if this was explicitly enabled by user via `"enableReturnData": true` in the config.
This PR fixes this issue.

Co-authored-by: Sina Mahmoodi <itz.s1na@gmail.com>

eth/tracers/logger/logger.go

@@ -418,6 +418,7 @@ type StructLogRes struct {
 	Depth         int                `json:"depth"`
 	Error         string             `json:"error,omitempty"`
 	Stack         *[]string          `json:"stack,omitempty"`
+	ReturnData    string             `json:"returnData,omitempty"`
 	Memory        *[]string          `json:"memory,omitempty"`
 	Storage       *map[string]string `json:"storage,omitempty"`
 	RefundCounter uint64             `json:"refund,omitempty"`
@@ -443,6 +444,9 @@ func formatLogs(logs []StructLog) []StructLogRes {
 			}
 			formatted[index].Stack = &stack
 		}
+		if trace.ReturnData != nil && len(trace.ReturnData) > 0 {
+			formatted[index].ReturnData = hexutil.Bytes(trace.ReturnData).String()
+		}
 		if trace.Memory != nil {
 			memory := make([]string, 0, (len(trace.Memory)+31)/32)
 			for i := 0; i+32 <= len(trace.Memory); i += 32 {