Use 'message' as the parameter name in FlMessageCodec::encode_message (#18253)

This is more consistent with the Dart code.
diff --git a/shell/platform/linux/fl_message_codec.cc b/shell/platform/linux/fl_message_codec.cc
index 79b82ec..fd13c5f 100644
--- a/shell/platform/linux/fl_message_codec.cc
+++ b/shell/platform/linux/fl_message_codec.cc
@@ -18,19 +18,19 @@
 static void fl_message_codec_init(FlMessageCodec* self) {}
 
 G_MODULE_EXPORT GBytes* fl_message_codec_encode_message(FlMessageCodec* self,
-                                                        FlValue* value,
+                                                        FlValue* message,
                                                         GError** error) {
   g_return_val_if_fail(FL_IS_MESSAGE_CODEC(self), nullptr);
 
   // If the user provided NULL, then make a temporary FlValue object for this to
   // make it simpler for the subclasses
   g_autoptr(FlValue) null_value = nullptr;
-  if (value == nullptr) {
+  if (message == nullptr) {
     null_value = fl_value_new_null();
-    value = null_value;
+    message = null_value;
   }
 
-  return FL_MESSAGE_CODEC_GET_CLASS(self)->encode_message(self, value, error);
+  return FL_MESSAGE_CODEC_GET_CLASS(self)->encode_message(self, message, error);
 }
 
 G_MODULE_EXPORT FlValue* fl_message_codec_decode_message(FlMessageCodec* self,
diff --git a/shell/platform/linux/public/flutter_linux/fl_message_codec.h b/shell/platform/linux/public/flutter_linux/fl_message_codec.h
index fb0862a..03e17db 100644
--- a/shell/platform/linux/public/flutter_linux/fl_message_codec.h
+++ b/shell/platform/linux/public/flutter_linux/fl_message_codec.h
@@ -60,18 +60,18 @@
   /**
    * FlMessageCodec::encode_message:
    * @codec: A #FlMessageCodec
-   * @value: value to encode or %NULL to encode the null value
+   * @message: message to encode or %NULL to encode the null value
    * @error: (allow-none): #GError location to store the error occurring, or
    * %NULL
    *
    * Virtual method to encode a message. A subclass must implement this method.
-   * If the subclass cannot handle the type of @value then it must generate a
+   * If the subclass cannot handle the type of @message then it must generate a
    * FL_MESSAGE_CODEC_ERROR_UNSUPPORTED_TYPE error.
    *
    * Returns: a binary message or %NULL on error.
    */
   GBytes* (*encode_message)(FlMessageCodec* codec,
-                            FlValue* value,
+                            FlValue* message,
                             GError** error);
 
   /**
@@ -97,15 +97,15 @@
  * fl_message_codec_encode_message:
  * @codec: a #FlMessageCodec
  * @buffer: buffer to write to
- * @value: value to encode or %NULL to encode the null value.
+ * @message: message to encode or %NULL to encode the null value.
  * @error: (allow-none): #GError location to store the error occurring, or %NULL
  *
- * Encode a value into a binary representation.
+ * Encode a message into a binary representation.
  *
  * Returns: a binary message or %NULL on error.
  */
 GBytes* fl_message_codec_encode_message(FlMessageCodec* codec,
-                                        FlValue* value,
+                                        FlValue* message,
                                         GError** error);
 
 /**
@@ -114,7 +114,7 @@
  * @message: binary message to decode
  * @error: (allow-none): #GError location to store the error occurring, or %NULL
  *
- * Decode a value from a binary encoding.
+ * Decode a message from a binary encoding.
  *
  * Returns: a #FlValue or %NULL on error.
  */