layout: Implement the fit-content() sizing function (#36056)

Spec: https://drafts.csswg.org/css-sizing-3/#funcdef-width-fit-content

It's similar to the `fit-content` keyword but, instead of clamping the
stretch size between `min-content` and `max-content`, it clamps the
provided argument.

So now that we support `fit-content`, it's quite straightforward to add.
It's just not completely clear what should happen when the argument has
a cyclic percentage, so this may need some further adjustments depending
on the outcome of https://github.com/w3c/csswg-drafts/issues/11805

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

components/layout_2020/flexbox/layout.rs

@@ -2599,11 +2599,8 @@ impl FlexItemBox {
                             BoxSizing::BorderBox => length - main_padding_border_sum,
                         }
                     };
-                    size.maybe_map(|v| {
-                        v.maybe_to_used_value(container_definite_main_size)
-                            .map(apply_box_sizing)
-                    })
-                    .unwrap_or_default()
+                    size.resolve_percentages_for_preferred(container_definite_main_size)
+                        .map(apply_box_sizing)
                 },
             },
         }