I don't like the word 'Enumize' in commit message. How about changing it to something like: (a) Add defines for logical replication protocol messages, or (b) Associate names with logical replication protocol messages.
I have used "Use Enum for top level logical replication message types" in the attached patch. But please free to use (a) if you feel so.
+ 2. It's easy to locate the code handling a given type.
In the above instead of 'type', shouldn't it be 'message'.
Used "message type". But please feel free to use "message" if you think that's appropriate.
Other than that the patch looks good to me.
Patch with updated commit message and also the list of reviewers