There's no built in functionality to do this. There may be a plugin but I don't know of one.
Why "Moderator" can't Edit Topic of Others?
This is one of the issue I am facing, where I created a group called "Moderator" and we are not able to give any special permission to them like, editing the topic or deleting it.
In this case; the "Moderator" reverted back and asked "What special permission does he has other than general users?"
Any help on this?