layout: Restrict stretch alignment to flex items with computed auto size (#36288)

We were allowing `align-self: stretch` to stretch flex items whose cross
size behaves as `auto`, including cyclic percentages.

However, https://github.com/w3c/csswg-drafts/issues/4525 resolved that
stretching should only happen when the cross size computes to `auto`.

So this patch exposes this information in `ContentBoxSizesAndPBM`, and
refactors the flexbox stretching logic.

Fixes: #36285

Testing:
 - `/css/css-flexbox/quirks-auto-block-size-with-percentage-item.html`
 - `/css/css-flexbox/stretch-requires-computed-auto-size.html`

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

tests/wpt/meta/MANIFEST.json

@@ -180356,6 +180356,19 @@
        {}
       ]
      ],
+     "stretch-requires-computed-auto-size.html": [
+      "01bc822af2a20636efe2d3a281ddaa41f5898906",
+      [
+       null,
+       [
+        [
+         "/css/reference/ref-filled-green-100px-square.xht",
+         "=="
+        ]
+       ],
+       {}
+      ]
+     ],
      "stretched-child-in-nested-flexbox.html": [
       "325d79e7c63f3e301c21f53f8bc97b48ae15c6b5",
       [

tests/wpt/meta/css/css-flexbox/quirks-auto-block-size-with-percentage-item.html.ini

@@ -1,3 +0,0 @@
-[quirks-auto-block-size-with-percentage-item.html]
-  [#container 1]
-    expected: FAIL