layout: Generalize ContainingBlock's block size to a SizeConstraint (#34946)

It used to be an `AuOrAuto`, turning it into a `SizeConstraint` allows
passing the information about the min and max constraints when the
containing block doesn't have a definite block size.

This will be useful for table layout.

Note that in most cases we were already constructing the containing
block from a `SizeConstraint`, but we were calling `to_auto_or()` to
turn it into an `AuOrAuto`.

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

components/layout_2020/replaced.rs

@@ -514,7 +514,7 @@ impl ReplacedContents {
         let block_stretch_size = containing_block
             .size
             .block
-            .non_auto()
+            .to_definite()
             .map(|block_size| Au::zero().max(block_size - pbm_sums.block));
 
         // First, compute the inline size. Intrinsic values depend on the block sizing properties