Loot table and feature ID use different names to refer to the same structure

Discovered while testing MC-248528, which is closely related.

The bug

The structure called "minecraft:monster_room" contains chests with a loot table named "minecraft:chests/simple_dungeon". As can be seen here, these IDs refer to the same structure by two different names, which is confusing.

How to reproduce

1. Use the command /placefeature minecraft:monster_room ~ ~ ~ while underground in Spectator mode near a cave (may require moving around a bit before it succeeds)

2. Note the structure which is placed, and the loot in its chests

3. Use the command /loot spawn ~ ~ ~ loot minecraft:chests/simple_dungeon

4. Note that this loot matches that of the aforementioned structure, despite said structure not having an ID of "simple_dungeon"

Expected results

The structure ID used by both of these would match.

Actual results

The same structure is referred to by two completely different names.

How to fix

Either the loot table should be renamed to "minecraft:chests/monster_room", the structure renamed to "minecraft:simple_dungeon", or both the loot table and the structure should be respectively renamed to "minecraft:chests/dungeon" and "minecraft:dungeon".