LibWeb: New start at layouting out the grid

According to the spec it's necessary to:
1. Layout the cells in the grid
2. Find the sizes of the rows and columns

Since I had started to do this backwards, and as I expand in future
commits, I take here the opportunity to start with a clean state.

The occupation_grid keeps track of which cells in the grid have been
filled out.

Userland/Libraries/LibWeb/Layout/GridFormattingContext.cpp

@@ -35,59 +35,10 @@ void GridFormattingContext::run(Box const& box, LayoutMode)
         return false;
     };
 
-    auto number_of_columns = (int)box.computed_values().grid_template_columns().size();
-    struct GridRow {
-        float height { 0 };
-        Vector<Box&> boxes;
-    };
-    Vector<GridRow> grid_rows;
-
-    auto current_column_count = 0;
-    box.for_each_child_of_type<Box>([&](Box& child_box) {
-        if (should_skip_is_anonymous_text_run(child_box))
-            return IterationDecision::Continue;
-
-        if (current_column_count == 0)
-            grid_rows.append(GridRow());
-        GridRow& grid_row = grid_rows.last();
-        grid_row.boxes.append(child_box);
-
-        auto& child_box_state = m_state.get_mutable(child_box);
-        if (child_box_state.content_height() > grid_row.height)
-            grid_row.height = child_box_state.content_height();
-        (void)layout_inside(child_box, LayoutMode::Normal);
-        if (child_box_state.content_height() > grid_row.height)
-            grid_row.height = child_box_state.content_height();
-
-        current_column_count++;
-        if (current_column_count == number_of_columns)
-            current_column_count = 0;
-        return IterationDecision::Continue;
-    });
-
-    auto& box_state = m_state.get_mutable(box);
-    float current_y_position = 0;
-    current_column_count = 0;
-    for (auto& grid_row : grid_rows) {
-        for (auto& child_box : grid_row.boxes) {
-            if (should_skip_is_anonymous_text_run(child_box))
-                continue;
-            auto& child_box_state = m_state.get_mutable(child_box);
-
-            // FIXME: instead of dividing the parent width equally between the columns, should use
-            // the values in the GridTrackSize objects.
-            child_box_state.set_content_width(box_state.content_width() / number_of_columns);
-            child_box_state.set_content_height(grid_row.height);
-            child_box_state.offset = { current_column_count * (box_state.content_width() / number_of_columns), current_y_position };
-
-            current_column_count++;
-            if (current_column_count == number_of_columns) {
-                current_y_position += grid_row.height;
-                current_column_count = 0;
-            }
-            continue;
-        }
-    }
-}
-
+    Vector<Vector<bool>> occupation_grid;
+    Vector<bool> occupation_grid_row;
+    for (int column_index = 0; column_index < max((int)box.computed_values().grid_template_columns().size(), 1); column_index++)
+        occupation_grid_row.append(false);
+    for (int row_index = 0; row_index < max((int)box.computed_values().grid_template_rows().size(), 1); row_index++)
+        occupation_grid.append(occupation_grid_row);
 }