ChunkGenerator#shouldGenerateStructures() doesn't fully work when #shouldGenerateDecorations() is false

Expected behavior

I expect structures to generate when I return true for shouldGenerateStructures()

Observed/Actual behavior

I noticed when doing some generator stuff, that structures aren't placed into the world when ChunkGenerator#shouldGenerateDecorations() return false.

I did some digging and came to the realization why this happens.
Structures are broken up into 2 parts:

1. StructureStarts = This is an early stage in the generation steps. Minecraft decides which types of structures will go where.
   When using shouldGenerateStructures returned as true... this stage decides it will place a structure there.

2. StructurePlacements = Later on in the chunk generation steps, in the same stage that decorations (features) are placed, the structure pieces are also placed.
   After seeing this in the code I realized if shouldGenerateDecorations returns false (thus preventing features from being placed), the structure piece placements are also skipped.

When this happens, the game will assume a structure is placed in a specific spot, this can be seen using the locate command (see steps below), where it'll find a structure, but nothing actually got placed.

Steps/models to reproduce

Simple code to replicate:

public void testGenerator() {
    WorldCreator worldCreator = new WorldCreator("world_test_for_paper");
    worldCreator.generator(new ChunkGenerator() {

        @Override
        public boolean shouldGenerateNoise() {
            return true; // Vanilla noise
        }

        @Override
        public boolean shouldGenerateSurface() {
            return true; // Vanilla surface
        }

        @Override
        public boolean shouldGenerateStructures() {
            return true; // Yes we want structures
        }

        @Override
        public boolean shouldGenerateDecorations() {
            return false; // No we dont want your trees
        }

        @Override
        public Location getFixedSpawnLocation(@NotNull World world, @NotNull Random random) {
            return new Location(world,1,1,1); // Speed up the process
        }
    });
    World testWorld = worldCreator.createWorld();
}

• start up server
• join server and teleport to new world
• run command /locate structure minecraft:village_plains
• Once the game finds the village, click the TP thing to TP to it.
• Behold, no village.

Plugin and Datapack List

[14:29:19 INFO]: ℹ Server Plugins (1):
[14:29:19 INFO]: Paper Plugins (1):
[14:29:19 INFO]:  - CorePlugin #(my plugin for testing)

Paper version

Currently using the 1.21.5 update branch:

[14:24:04 INFO]: This server is running Paper version 1.21.5-DEV-update/1.21.5@ce91a8c (1970-01-01T00:00:00Z) (Implementing API version 1.21.5-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.5-DEV-b6d70a9 (MC: 1.21.5)

I believe this would also happen on previous versions.
I'm pretty sure this happened to me in 1.21.4 and just forgot to report it.

Other

I'm open to doing a PR for this.
Looking thru the code I feel like this could potentially be a simple fix.
I wanted to wait til after 1.21.5 was released, as I'm sure you guys have too much on your plate as it is.

Start with ChunkGenerator#shouldGenerateStructures() and ChunkGenerator#shouldGenerateDecorations(), then trace the generation stages described in the report. Reproduce the issue with the supplied WorldCreator generator, use /locate structure minecraft:village_plains, and verify that structure pieces are placed even when decorations are disabled.