Kernel: Add Memory::RegionTree to share code between AddressSpace and MM

RegionTree holds an IntrusiveRedBlackTree of Region objects and vends a
set of APIs for allocating memory ranges.

It's used by AddressSpace at the moment, and will be used by MM soon.

Kernel/Memory/RegionTree.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/IntrusiveRedBlackTree.h>
+#include <Kernel/Memory/Region.h>
+#include <Kernel/Memory/VirtualRange.h>
+#include <Kernel/VirtualAddress.h>
+
+namespace Kernel::Memory {
+
+class RegionTree {
+    AK_MAKE_NONCOPYABLE(RegionTree);
+    AK_MAKE_NONMOVABLE(RegionTree);
+
+public:
+    explicit RegionTree(VirtualRange total_range)
+        : m_total_range(total_range)
+    {
+    }
+
+    ~RegionTree();
+
+    auto& regions() { return m_regions; }
+    auto const& regions() const { return m_regions; }
+
+    VirtualRange total_range() const { return m_total_range; }
+
+    ErrorOr<VirtualRange> try_allocate_anywhere(size_t size, size_t alignment = PAGE_SIZE);
+    ErrorOr<VirtualRange> try_allocate_specific(VirtualAddress base, size_t size);
+    ErrorOr<VirtualRange> try_allocate_randomized(size_t size, size_t alignment = PAGE_SIZE);
+
+    void delete_all_regions_assuming_they_are_unmapped();
+
+private:
+    IntrusiveRedBlackTree<&Region::m_tree_node> m_regions;
+    VirtualRange const m_total_range;
+};
+
+}