layout: Fix intrinsic contributions of anonymous blocks (#34719)

In order to compute the inline min-content and max-content contributions
of an anonymous block, we were finding its min-content and max-content
inline size with a SizeConstraint coming from the block size of the box.

However, anonymous blocks do not establish a containing block for their
contents, so this patch uses a SizeConstraint from the block size of the
containing block.

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

components/layout_2020/geom.rs

@@ -871,6 +871,14 @@ impl SizeConstraint {
     }
 }
 
+impl From<AuOrAuto> for SizeConstraint {
+    fn from(size: AuOrAuto) -> Self {
+        size.non_auto()
+            .map(SizeConstraint::Definite)
+            .unwrap_or_default()
+    }
+}
+
 #[derive(Clone, Default)]
 pub(crate) struct Sizes {
     /// <https://drafts.csswg.org/css-sizing-3/#preferred-size-properties>