Add Support for Async Tab Completions for Paper Servers

This adds the ability for plugins to define completion handlers as async safe (not on games main thread)

When they are defined async safe, and ran on a Paper 1.12.2+ server, with a Paper ACF manager,
completions will be handled mostly async, letting you safely do heavier operations in tab completions.

bungee/src/main/java/co/aikar/commands/BungeeCommandCompletions.java

@@ -39,7 +39,7 @@ public class BungeeCommandCompletions extends CommandCompletions<BungeeCommandCo
 
     public BungeeCommandCompletions(CommandManager manager) {
         super(manager);
-        registerCompletion("chatcolors", c -> {
+        registerAsyncCompletion("chatcolors", c -> {
             Stream<ChatColor> colors = Stream.of(ChatColor.values());
             if (c.hasConfig("colorsonly")) {
                 colors = colors.filter(color -> color.ordinal() <= 0xF);

bungee/src/main/java/co/aikar/commands/BungeeCommandIssuer.java

@@ -24,7 +24,6 @@
 package co.aikar.commands;
 
 import net.md_5.bungee.api.CommandSender;
-import net.md_5.bungee.api.chat.TextComponent;
 import net.md_5.bungee.api.connection.ProxiedPlayer;
 
 import java.util.Objects;

bungee/src/main/java/co/aikar/commands/BungeeCommandManager.java

@@ -30,9 +30,9 @@ import net.md_5.bungee.api.plugin.Plugin;
 
 import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.HashMap;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 

bungee/src/main/java/co/aikar/commands/BungeeRootCommand.java

@@ -29,10 +29,8 @@ import net.md_5.bungee.api.CommandSender;
 import net.md_5.bungee.api.plugin.Command;
 import net.md_5.bungee.api.plugin.TabExecutor;
 
-import java.util.List;
 import java.util.ArrayList;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.List;
 
 public class BungeeRootCommand extends Command implements RootCommand, TabExecutor {
 
@@ -73,6 +71,11 @@ public class BungeeRootCommand extends Command implements RootCommand, TabExecut
         return subCommands;
     }
 
+    @Override
+    public List<BaseCommand> getChildren() {
+        return children;
+    }
+
     @Override
     public void execute(CommandSender sender, String[] args) {
         execute(manager.getCommandIssuer(sender), getName(), args);
@@ -80,13 +83,7 @@ public class BungeeRootCommand extends Command implements RootCommand, TabExecut
 
     @Override
     public Iterable<String> onTabComplete(CommandSender commandSender, String[] strings) {
-        return onTabComplete(manager.getCommandIssuer(commandSender), getName(), strings);
-    }
-
-    private List<String> onTabComplete(CommandIssuer sender, String alias, String[] args) throws IllegalArgumentException {
-        Set<String> completions = new HashSet<>();
-        this.children.forEach(child -> completions.addAll(child.tabComplete(sender, alias, args)));
-        return new ArrayList<>(completions);
+        return getTabCompletions(manager.getCommandIssuer(commandSender), getName(), strings);
     }
 
     @Override