Feature summary (what you would like to be able to do and where):

Special:MergeHistory shouldn't copy the watchlist from the source page to the destination page. Or maybe it should do so only when doing a full merge and turning the source into a redirect to the destination

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

Especially with T382958 now deployed, the fact that some revisions from long ago were merged from one page to another does not mean watchers of the first page are necessarily interested in the second one - the second page is often a meaningless holding pen or temporary page.

Benefits (why should this be implemented?):

Less confusion on people's watchlists. This was brought up in the Wikimedia Community Discord server.