LibWeb: Add GridTrackPlacement for grid-[column/row]-[start/end]

Add GridTrackPlacement to use with grid-column-start and related CSS
properties.

Userland/Libraries/LibWeb/CSS/GridTrackPlacement.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2022, Martin Falisse <mfalisse@outlook.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace Web::CSS {
+
+class GridTrackPlacement {
+public:
+    GridTrackPlacement(int, bool);
+    GridTrackPlacement(int);
+    GridTrackPlacement();
+
+    static GridTrackPlacement make_auto() { return GridTrackPlacement(); };
+
+    void set_position(int position) { m_position = position; }
+    int position() const { return m_position; }
+
+    void set_has_span(bool has_span) { m_has_span = has_span; }
+    bool has_span() const { return m_has_span; }
+
+    String to_string() const;
+    bool operator==(GridTrackPlacement const& other) const
+    {
+        return m_position == other.position() && m_has_span == other.has_span();
+    }
+
+private:
+    int m_position { 0 };
+    bool m_has_span { false };
+};
+
+}