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/sizing.rs

@@ -191,6 +191,10 @@ pub(crate) fn outer_inline(
                 content_size.sizes.max_content,
                 content_size.depends_on_block_constraints,
             ),
+            Size::FitContentFunction(size) => {
+                let size = content_size.sizes.shrink_to_fit(size);
+                (size, size, content_size.depends_on_block_constraints)
+            },
             Size::Stretch => return stretch_values,
         })
     };