layout: Allow collapsing bottom margins with any indefinite block size (#36278)

According to CSS2, the bottom margin of a block container can collapse
with the bottom margin of its last in-flow child if `height` computes to
`auto`.

However, according to CSS Sizing, that was "legacy spec prose" and
should be interpreted as "behaves as `auto`".

Therefore, cyclic percentages and intrinsic keywords like `min-content`
shouldn't prevent margin collapse, because they behave as `auto`.

This change aligns Servo with Gecko and Blink, but diverges from WebKit.

https://www.w3.org/TR/CSS22/box.html#collapsing-margins
https://www.w3.org/TR/css-sizing/#behave-auto

Testing:
-
`tests/wpt/tests/css/css-sizing/margin-collapse-with-indefinite-block-size-001.html`
-
`tests/wpt/tests/css/css-sizing/margin-collapse-with-indefinite-block-size-002.html`
-
`tests/wpt/tests/css/css-sizing/margin-collapse-with-indefinite-block-size-003.html`
-
`tests/wpt/tests/css/css-sizing/margin-collapse-with-indefinite-block-size-004.html`
-
`tests/wpt/tests/css/css-sizing/margin-collapse-with-indefinite-block-size-005.html`

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

components/layout_2020/flow/mod.rs

@@ -1012,7 +1012,7 @@ fn layout_in_flow_non_replaced_block_level_same_formatting_context(
     let end_margin_can_collapse_with_children = collapsed_through ||
         (pbm.padding.block_end == Au::zero() &&
             pbm.border.block_end == Au::zero() &&
-            computed_block_size.is_auto());
+            !containing_block_for_children.size.block.is_definite());
     if end_margin_can_collapse_with_children {
         block_margins_collapsed_with_children
             .end