layout: Let stretch on flex item cross size stretch to the line (#38526)

We were instead stretching to the containing block, which implied that
the behaviors of a `stretch` size and `stretch` alignment weren't
consistent.

As resolved by the CSSWG, the behavior will now be:
 - If the cross size of the line is known, stretch to the line.
 - Otherwise, stretch to the containing block.

See https://github.com/w3c/csswg-drafts/issues/11784

This aligns us with Blink, which has already shipped this new behavior.

Testing: Improves existing WPT and adds a new test.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

components/layout/replaced.rs

@@ -471,7 +471,9 @@ impl ReplacedContents {
             collapsible_margins_in_children: CollapsedBlockMargins::zero(),
             content_block_size,
             content_inline_size_for_table: None,
-            depends_on_block_constraints: false,
+            // The result doesn't depend on `containing_block_for_children.size.block`,
+            // but it depends on `lazy_block_size`, which is probably tied to that.
+            depends_on_block_constraints: true,
             fragments: self.make_fragments(layout_context, &base.style, size),
             specific_layout_info: None,
         }