LibWeb: Don't collapse horizontal margins between floating boxes

CSS 2.2 says "Horizontal margins never collapse."

So instead of collapsing them, we now add them together, which makes
negative margins between floating boxes work beautifully.

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -601,12 +601,8 @@ void BlockFormattingContext::layout_floating_box(Box const& box, BlockContainer
         place_block_level_element_in_normal_flow_horizontally(box, containing_block);
     }
 
+    // Then we float it to the left or right.
     auto float_box = [&](FloatSide side, FloatSideData& side_data) {
-        auto first_edge = [&](FormattingState::NodeState const& thing) { return side == FloatSide::Left ? thing.margin_left : thing.margin_right; };
-        auto second_edge = [&](FormattingState::NodeState const& thing) { return side == FloatSide::Right ? thing.margin_left : thing.margin_right; };
-
-        // Then we float it to the left or right.
-
         float offset_from_edge = 0;
         auto float_to_edge = [&] {
             if (side == FloatSide::Left)
@@ -625,29 +621,16 @@ void BlockFormattingContext::layout_floating_box(Box const& box, BlockContainer
             side_data.y_offset = 0;
         } else {
             auto& previous_box = side_data.current_boxes.last();
-            auto const& previous_box_state = m_state.get(previous_box.box);
-
-            auto margin_collapsed_with_previous = max(
-                second_edge(previous_box_state),
-                first_edge(box_state));
 
             float wanted_offset_from_edge = 0;
             bool fits_on_line = false;
 
             if (side == FloatSide::Left) {
-                auto previous_right_edge = side_data.current_width
-                    - previous_box_state.margin_right
-                    + margin_collapsed_with_previous;
-
-                wanted_offset_from_edge = previous_right_edge + box_state.border_left + box_state.padding_left;
-                fits_on_line = (wanted_offset_from_edge + box_state.content_width + box_state.padding_right + box_state.border_right + box_state.margin_right) <= width_of_containing_block;
+                wanted_offset_from_edge = side_data.current_width + box_state.margin_box_left();
+                fits_on_line = (wanted_offset_from_edge + box_state.content_width + box_state.margin_box_right()) <= width_of_containing_block;
             } else {
-                auto previous_left_edge = side_data.current_width
-                    - previous_box_state.margin_left
-                    + margin_collapsed_with_previous;
-
-                wanted_offset_from_edge = previous_left_edge + box_state.border_right + box_state.padding_right + box_state.content_width;
-                fits_on_line = (wanted_offset_from_edge - box_state.padding_left - box_state.border_left - box_state.margin_left) >= 0;
+                wanted_offset_from_edge = side_data.current_width + box_state.margin_box_right() + box_state.content_width;
+                fits_on_line = (wanted_offset_from_edge - box_state.margin_box_left()) >= 0;
             }
 
             if (fits_on_line) {