Add Folia scheduler adapter with folia check support;

(cherry picked from commit 7dd04ccc1b)

worldguard-bukkit/src/main/java/com/sk89q/worldguard/bukkit/scheduler/FoliaSchedulerAdapter.java

@@ -0,0 +1,19 @@
+package com.sk89q.worldguard.bukkit.scheduler;
+
+public class FoliaSchedulerAdapter {
+
+  private static final boolean SUPPORTED = checkSupport();
+
+  public static boolean isSupported() {
+    return SUPPORTED;
+  }
+
+  private static boolean checkSupport() {
+    try {
+      Class.forName("io.papermc.paper.threadedregions.RegionizedServer");
+      return true;
+    } catch (ClassNotFoundException e) {
+      return false;
+    }
+  }
+}