Strangling underwater_* in the crib

BUR #34461 has been rejected.

create alias underwater_house -> underwater_structure
create alias underwater_shrine -> underwater_structure

underwater_structure can be a catch-all tag. underwater_structure shrine should ideally show pics of underwater shrines.
underwater_city is a bit unique, so I'll leave that aside.

Structure is a pretty broad term, might there not be reason to differentiate underwater buildings and non-building structures?

The number of tags per search for anyone lower than platinum rank is limited.

Unless there's a good reason to make the life of low-ranking members (plus non-members) harder than as-is, I'd rather just make underwater_shrine auto-implicate underwater structure and shrine.

These are both fairly unique/frequently drawn (a lot of these aren't tagged with these) concepts, and underwater_structure feels like one of those tags that ends up tagging things that are meant to be underwater.

If they don't require their own tags, however, I'm not sure structure adds much; immersed + x would probably cover anything that underwater_structure + x does, if applied properly?

The bulk update request #34461 (forum #322257) has been rejected by @nonamethanks.