LibWeb: Express intrinsic size layout via size constraints

Previously, we had three layout modes:

- Normal:
    - Everything uses the computed values from CSS.

- MinContent:
    - Containing blocks act as if they have 0 width.
    - All line breaking opportunities are taken.

- MaxContent:
    - Containing blocks act as if they have infinite width.
    - Only forced line breaks are accepted.

The above was based on a set of misunderstandings of CSS sizing.
A major problem with the above was that *all* containing blocks
behaved differently during intrinsic size layout, not just the
relevant one.

With this patch there are only two layout modes:

- Normal:
    - Everything uses the computed values from CSS.

- IntrinsicSizeDetermination:
    - One or more boxes have size constraints applied.

There are two size constraints per layout box, set here:

- FormattingState::NodeState::width_constraint
- FormattingState::NodeState::height_constraint

They are of type SizeConstraint and can be one of None, MinContent,
or MaxContent. The default is None.

When performing an IntrinsicSizeDetermination layout, we now assign
a size constraint to the box we're trying to determine the intrinsic
size of, which is then honored by using two new helpers to query
the dimensions of containing blocks:

- FormattingContext::containing_block_width_for(Box)
- FormattingContext::containing_block_height_for(Box)

If there's a relevant constraint in effect on the Box, the size of
its containing block is adjusted accordingly.

This is essentially an implementation of the "available space"
constraints from CSS-SIZING-3. I'm sure some things will break from
this, and we'll have to deal with that separately.

Spec: https://drafts.csswg.org/css-sizing-3/#available

Userland/Libraries/LibWeb/Layout/LineBuilder.cpp

@@ -36,16 +36,16 @@ void LineBuilder::begin_new_line(bool increment_y)
     if (increment_y)
         m_current_y += max(m_max_height_on_current_line, m_context.containing_block().line_height());
 
-    switch (m_layout_mode) {
-    case LayoutMode::Normal:
-        m_available_width_for_current_line = m_context.available_space_for_line(m_current_y);
-        break;
-    case LayoutMode::MinContent:
+    switch (m_containing_block_state.width_constraint) {
+    case SizeConstraint::MinContent:
         m_available_width_for_current_line = 0;
         break;
-    case LayoutMode::MaxContent:
+    case SizeConstraint::MaxContent:
         m_available_width_for_current_line = INFINITY;
         break;
+    default:
+        m_available_width_for_current_line = m_context.available_space_for_line(m_current_y);
+        break;
     }
     m_max_height_on_current_line = 0;
 
@@ -79,12 +79,8 @@ void LineBuilder::append_text_chunk(TextNode const& text_node, size_t offset_in_
     m_max_height_on_current_line = max(m_max_height_on_current_line, content_height);
 }
 
-bool LineBuilder::should_break(LayoutMode layout_mode, float next_item_width)
+bool LineBuilder::should_break(float next_item_width)
 {
-    if (layout_mode == LayoutMode::MinContent)
-        return true;
-    if (layout_mode == LayoutMode::MaxContent)
-        return false;
     auto const& line_boxes = m_containing_block_state.line_boxes;
     if (line_boxes.is_empty() || line_boxes.last().is_empty())
         return false;