Add ServerResourcePackRemoveEvent (#1379)

* Add ServerResourcePackRemoveEvent

* Add nonnull check

* Fix indentation

* Fix import code style

api/src/main/java/com/velocitypowered/api/event/player/ServerResourcePackRemoveEvent.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2018-2023 Velocity Contributors
+ *
+ * The Velocity API is licensed under the terms of the MIT License. For more details,
+ * reference the LICENSE file in the api top-level directory.
+ */
+
+package com.velocitypowered.api.event.player;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.event.ResultedEvent;
+import com.velocitypowered.api.event.annotation.AwaitingEvent;
+import com.velocitypowered.api.proxy.ServerConnection;
+import java.util.UUID;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * This event is fired when the downstream server tries to remove a resource pack from player
+ * or clear all of them. The proxy will wait on this event to finish before forwarding the
+ * action to the user. If this event is denied, no resource packs will be removed from player.
+ */
+@AwaitingEvent
+public class ServerResourcePackRemoveEvent implements ResultedEvent<ResultedEvent.GenericResult> {
+
+  private GenericResult result;
+  private final @MonotonicNonNull UUID packId;
+  private final ServerConnection serverConnection;
+
+  /**
+   * Instantiates this event.
+   */
+  public ServerResourcePackRemoveEvent(UUID packId, ServerConnection serverConnection) {
+    this.result = ResultedEvent.GenericResult.allowed();
+    this.packId = packId;
+    this.serverConnection = serverConnection;
+  }
+
+  /**
+   * Returns the id of the resource pack, if it's null all the resource packs
+   * from player will be cleared.
+   *
+   * @return the id
+   */
+  @Nullable
+  public UUID getPackId() {
+    return packId;
+  }
+
+  /**
+   * Returns the server that tries to remove a resource pack from player or clear all of them.
+   *
+   * @return the server connection
+   */
+  public ServerConnection getServerConnection() {
+    return serverConnection;
+  }
+
+  @Override
+  public GenericResult getResult() {
+    return this.result;
+  }
+
+  @Override
+  public void setResult(GenericResult result) {
+    this.result = Preconditions.checkNotNull(result, "result");
+  }
+}