Add GUI regression test for code in doc blocks

Author: GuillaumeGomez

tests/rustdoc-gui/check-stab-in-docblock.goml

@@ -1,5 +1,5 @@
 // This test checks that using `.stab` attributes in `.docblock` elements doesn't
-// create scrollable paragraphs.
+// create scrollable paragraphs and is correctly displayed (not making weird blocks).
 go-to: "file://" + |DOC_PATH| + "/test_docs/index.html"
 // Needs the text to be display to check for scrollable content.
 show-text: true
@@ -31,3 +31,15 @@ assert-property: (
     ".top-doc .docblock p:nth-of-type(3)",
     {"scrollHeight": |clientHeight|, "scrollWidth": |clientWidth|},
 )
+
+// Ensure that `<code>` elements in code don't make big blocks.
+compare-elements-size-near: (
+    "#reexport\.TheStdReexport > code",
+    ".docblock p span[data-span='1']",
+    {"height": 1},
+)
+compare-elements-size-near: (
+    "#reexport\.TheStdReexport > code",
+    ".docblock p span[data-span='2']",
+    {"height": 1},
+)