AK: Add a FixedArray<T> container

This is a simple array wrapper that knows its size. It has begin/end
so you can use range-for. It also has a resize() that reallocates.

AK/FixedArray.h

@@ -0,0 +1,83 @@
+#pragma once
+
+#include <AK/Vector.h>
+
+namespace AK {
+
+template<typename T>
+class FixedArray {
+public:
+    FixedArray() {}
+    explicit FixedArray(size_t size)
+        : m_size(size)
+    {
+        m_elements = (T*)kmalloc(sizeof(T) * m_size);
+        for (size_t i = 0; i < m_size; ++i)
+            new (&m_elements[i]) T();
+    }
+    ~FixedArray()
+    {
+        clear();
+    }
+
+    FixedArray(const FixedArray& other)
+        : m_size(other.m_size)
+    {
+        m_elements = (T*)kmalloc(sizeof(T) * m_size);
+        for (size_t i = 0; i < m_size; ++i)
+            new (&m_elements[i]) T(other[i]);
+    }
+
+    FixedArray& operator=(const FixedArray&) = delete;
+    FixedArray(FixedArray&&) = delete;
+    FixedArray& operator=(FixedArray&&) = delete;
+
+    void clear()
+    {
+        if (!m_elements)
+            return;
+        for (size_t i = 0; i < m_size; ++i)
+            m_elements[i].~T();
+        kfree(m_elements);
+        m_elements = nullptr;
+        m_size = 0;
+    }
+
+    size_t size() const { return m_size; }
+
+    T& operator[](size_t index) { return m_elements[index]; }
+    const T& operator[](size_t index) const { return m_elements[index]; }
+
+    void resize(size_t new_size)
+    {
+        if (new_size == m_size)
+            return;
+        auto* new_elements = (T*)kmalloc(new_size * sizeof(T));
+        for (size_t i = 0; i < min(new_size, m_size); ++i)
+            new (&new_elements[i]) T(move(m_elements[i]));
+        for (size_t i = min(new_size, m_size); i < new_size; ++i)
+            new (&new_elements[i]) T();
+        for (size_t i = 0; i < m_size; ++i)
+            m_elements[i].~T();
+        if (m_elements)
+            kfree(m_elements);
+        m_elements = new_elements;
+        m_size = new_size;
+    }
+
+    using Iterator = VectorIterator<FixedArray, T>;
+    Iterator begin() { return Iterator(*this, 0); }
+    Iterator end() { return Iterator(*this, size()); }
+
+    using ConstIterator = VectorIterator<const FixedArray, const T>;
+    ConstIterator begin() const { return ConstIterator(*this, 0); }
+    ConstIterator end() const { return ConstIterator(*this, size()); }
+
+private:
+    size_t m_size { 0 };
+    T* m_elements { nullptr };
+};
+
+}
+
+using AK::FixedArray;