Add datapack registration lifecycle event (#11804)

paper-server/patches/sources/net/minecraft/server/commands/ReloadCommand.java.patch

@@ -9,6 +9,15 @@
              LOGGER.warn("Failed to execute reload", throwable);
              source.sendFailure(Component.translatable("commands.reload.failure"));
              return null;
+@@ -24,7 +_,7 @@
+     }
+ 
+     private static Collection<String> discoverNewPacks(PackRepository packRepository, WorldData worldData, Collection<String> selectedIds) {
+-        packRepository.reload();
++        packRepository.reload(true); // Paper - will perform a full reload
+         Collection<String> list = Lists.newArrayList(selectedIds);
+         Collection<String> disabled = worldData.getDataConfiguration().dataPacks().getDisabled();
+ 
 @@ -36,6 +_,16 @@
  
          return list;