LibGfx: Add Gfx::Path, a basic 2D path with <canvas> semantics

This will be used to implement painting of 2D paths. This first patch
adds support for line_to(), move_to() and close().

It will try to have the same semantics as the HTML <canvas> element.

To stroke a Path, simply pass it to Painter::stroke_path().

Libraries/LibGfx/Path.h

@@ -0,0 +1,75 @@
+/*
+ * 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
+
+#include <AK/Vector.h>
+#include <LibGfx/FloatPoint.h>
+#include <LibGfx/Forward.h>
+
+namespace Gfx {
+
+class Path {
+public:
+    struct Segment {
+        enum class Type {
+            Invalid,
+            MoveTo,
+            LineTo,
+        };
+
+        Type type { Type::Invalid };
+        FloatPoint point;
+    };
+
+    Path() {}
+
+    void move_to(const FloatPoint& point)
+    {
+        m_segments.append({ Segment::Type::MoveTo, point });
+    }
+
+    void line_to(const FloatPoint& point)
+    {
+        m_segments.append({ Segment::Type::LineTo, point });
+    }
+
+    void close();
+
+    const Vector<Segment>& segments() const { return m_segments; }
+
+    String to_string() const;
+
+private:
+    Vector<Segment> m_segments;
+};
+
+inline const LogStream& operator<<(const LogStream& stream, const Path& path)
+{
+    return stream << path.to_string();
+}
+
+}