Add and call RegionizedServerInitEvent from Folia (#13034)

paper-api/src/main/java/io/papermc/paper/threadedregions/RegionizedServerInitEvent.java

@@ -0,0 +1,25 @@
+package io.papermc.paper.threadedregions;
+
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.server.ServerEvent;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * This event is called after the server is initialised but <b>before</b> the server begins ticking regions in parallel.
+ * Plugins may use this as a hook to run post initialisation logic without worrying about the possibility that
+ * regions are ticking in parallel.
+ */
+@NullMarked
+public class RegionizedServerInitEvent extends ServerEvent {
+
+    private static final HandlerList handlers = new HandlerList();
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}

paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch

@@ -747,7 +747,7 @@
      protected void runServer() {
          try {
              if (!this.initServer()) {
-@@ -675,6 +_,35 @@
+@@ -675,6 +_,36 @@
              this.statusIcon = this.loadStatusIcon().orElse(null);
              this.status = this.buildServerStatus();
  
@@ -755,6 +755,7 @@
 +            // Spigot start
 +            // Paper start
 +            LOGGER.info("Running delayed init tasks");
++            new io.papermc.paper.threadedregions.RegionizedServerInitEvent().callEvent(); // Call Folia init event
 +            this.server.getScheduler().mainThreadHeartbeat(); // run all 1 tick delay tasks during init,
 +            // this is going to be the first thing the tick process does anyways, so move done and run it after
 +            // everything is init before watchdog tick.