SPIGOT-7261: Add AsyncStructureSpawnEvent

By: Lauriichan <laura.endress@syntaxphoenix.com>

paper-server/nms-patches/net/minecraft/world/level/StructureManager.patch

@@ -0,0 +1,11 @@
+--- a/net/minecraft/world/level/StructureManager.java
++++ b/net/minecraft/world/level/StructureManager.java
+@@ -32,7 +32,7 @@
+ 
+ public class StructureManager {
+ 
+-    private final GeneratorAccess level;
++    public final GeneratorAccess level; // PAIL private -> public
+     private final WorldOptions worldOptions;
+     private final StructureCheck structureCheck;
+ 

paper-server/nms-patches/net/minecraft/world/level/chunk/ChunkGenerator.patch

@@ -61,3 +61,18 @@
      private static StructureBoundingBox getWritableArea(IChunkAccess ichunkaccess) {
          ChunkCoordIntPair chunkcoordintpair = ichunkaccess.getPos();
          int i = chunkcoordintpair.getMinBlockX();
+@@ -576,6 +603,14 @@
+         StructureStart structurestart = structure.generate(iregistrycustom, this, this.biomeSource, randomstate, structuretemplatemanager, i, chunkcoordintpair, j, ichunkaccess, predicate);
+ 
+         if (structurestart.isValid()) {
++            // CraftBukkit start
++            StructureBoundingBox box = structurestart.getBoundingBox();
++            org.bukkit.event.world.AsyncStructureSpawnEvent event = new org.bukkit.event.world.AsyncStructureSpawnEvent(structuremanager.level.getMinecraftWorld().getWorld(), org.bukkit.craftbukkit.generator.strucutre.CraftStructure.minecraftToBukkit(structure, iregistrycustom), new org.bukkit.util.BoundingBox(box.minX(), box.minY(), box.minZ(), box.maxX(), box.maxY(), box.maxZ()), chunkcoordintpair.x, chunkcoordintpair.z);
++            org.bukkit.Bukkit.getPluginManager().callEvent(event);
++            if (event.isCancelled()) {
++                return true;
++            }
++            // CraftBukkit end
+             structuremanager.setStartForStructure(sectionposition, structure, structurestart, ichunkaccess);
+             return true;
+         } else {