Auto merge of #29755 - stshine:automatic-min-size, r=Loirooriol

layout_2020: Implement automatic minimum size of flex items

Implement the algorithm described in
https://drafts.csswg.org/css-flexbox/#min-size-auto.

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components/layout_2020/replaced.rs

@@ -201,7 +201,7 @@ impl ReplacedContent {
         Vec2::from_physical_size(&intrinsic_size, style.writing_mode)
     }
 
-    fn inline_size_over_block_size_intrinsic_ratio(
+    pub fn inline_size_over_block_size_intrinsic_ratio(
         &self,
         style: &ComputedValues,
     ) -> Option<CSSFloat> {