layout: Allow lazy resolution of automatic minimum sizes (#35965)

`Size::resolve_for_min()` had an `Au` parameter, representing the value
to be used for an automatic minimum size. However, this amount isn't
trivial to compute in flexbox, so this patch changes the parameter to a
function that can be called lazily.

Note flexbox isn't currently using `Size::resolve_for_min()`, but it
will in #35961.

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

components/layout_2020/positioned.rs

@@ -793,7 +793,7 @@ impl AbsoluteAxisSolver<'_> {
                 SizeConstraint::Definite(self.computed_sizes.resolve(
                     self.axis,
                     initial_behavior,
-                    Au::zero(),
+                    Au::zero,
                     Some(stretch_size),
                     get_content_size,
                     self.is_table,