accounts/abi: change unpacking of abi fields w/ underscores (#16513)

* accounts/abi: fix name styling when unpacking abi fields w/ underscores

ABI fields with underscores that are being unpacked
into structs expect structs with following form:

int_one -> Int_one

whereas in abigen the generated structs are camelcased

int_one -> IntOne

so updated the unpack method to expect camelcased structs as well.

accounts/abi/argument.go

@@ -272,14 +272,13 @@ func (arguments Arguments) Pack(args ...interface{}) ([]byte, error) {
 	return ret, nil
 }
 
-// capitalise makes the first character of a string upper case, also removing any
-// prefixing underscores from the variable names.
-func capitalise(input string) string {
-	for len(input) > 0 && input[0] == '_' {
-		input = input[1:]
+// ToCamelCase converts an under-score string to a camel-case string
+func ToCamelCase(input string) string {
+	parts := strings.Split(input, "_")
+	for i, s := range parts {
+		if len(s) > 0 {
+			parts[i] = strings.ToUpper(s[:1]) + s[1:]
+		}
 	}
-	if len(input) == 0 {
-		return ""
-	}
-	return strings.ToUpper(input[:1]) + input[1:]
+	return strings.Join(parts, "")
 }