LibDraw: Introduce (formerly known as SharedGraphics.)

Instead of LibGUI and WindowServer building their own copies of the drawing
and graphics code, let's it in a separate LibDraw library.

This avoids building the code twice, and will encourage better separation
of concerns. :^)

Libraries/LibDraw/DisjointRectSet.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <AK/Vector.h>
+#include <LibDraw/Rect.h>
+
+class DisjointRectSet {
+public:
+    DisjointRectSet() {}
+    ~DisjointRectSet() {}
+    DisjointRectSet(DisjointRectSet&& other)
+        : m_rects(move(other.m_rects))
+    {
+    }
+
+    void add(const Rect&);
+
+    bool is_empty() const { return m_rects.is_empty(); }
+    int size() const { return m_rects.size(); }
+
+    void clear() { m_rects.clear(); }
+    void clear_with_capacity() { m_rects.clear_with_capacity(); }
+    const Vector<Rect, 32>& rects() const { return m_rects; }
+
+private:
+    void shatter();
+
+    Vector<Rect, 32> m_rects;
+};