Kernel: Add forward declaration header

Kernel/Forward.h

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+namespace Kernel {
+
+class BlockDevice;
+class CharacterDevice;
+class Custody;
+class Device;
+class DiskCache;
+class DoubleBuffer;
+class File;
+class FileDescription;
+class IPv4Socket;
+class Inode;
+class InodeIdentifier;
+class InodeVMObject;
+class InodeWatcher;
+class KBuffer;
+class KResult;
+class LocalSocket;
+class PageDirectory;
+class PhysicalPage;
+class PhysicalRegion;
+class Process;
+class ProcessInspectionHandle;
+class ProcessTracer;
+class Range;
+class RangeAllocator;
+class Region;
+class Scheduler;
+class SharedBuffer;
+class Socket;
+class TCPSocket;
+class Thread;
+class UDPSocket;
+class VMObject;
+class WaitQueue;
+
+template<typename T>
+class KResultOr;
+
+}