Kernel: Make VirtualFileSystem::Mount a top-level class

And move it to its own compilation unit.

Kernel/FileSystem/Mount.cpp

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/FileSystem/Custody.h>
+#include <Kernel/FileSystem/FileSystem.h>
+#include <Kernel/FileSystem/Inode.h>
+#include <Kernel/FileSystem/Mount.h>
+
+namespace Kernel {
+
+Mount::Mount(FileSystem& guest_fs, Custody* host_custody, int flags)
+    : m_guest(guest_fs.root_inode())
+    , m_guest_fs(guest_fs)
+    , m_host_custody(host_custody)
+    , m_flags(flags)
+{
+}
+
+Mount::Mount(Inode& source, Custody& host_custody, int flags)
+    : m_guest(source)
+    , m_guest_fs(source.fs())
+    , m_host_custody(host_custody)
+    , m_flags(flags)
+{
+}
+
+String Mount::absolute_path() const
+{
+    if (!m_host_custody)
+        return "/";
+    return m_host_custody->absolute_path();
+}
+
+Inode* Mount::host()
+{
+    if (!m_host_custody)
+        return nullptr;
+    return &m_host_custody->inode();
+}
+
+Inode const* Mount::host() const
+{
+    if (!m_host_custody)
+        return nullptr;
+    return &m_host_custody->inode();
+}
+
+}