Give the CommonMark blocks a directive form for what their spelling cannot hold

corpus/round-trip/block-nodes/code-block-attributes.md

@@ -0,0 +1,23 @@
+:::codeBlock {hideLineNumbers=true localId=01a0431d-201b-70a7-81fa-8d0072e09eab uniqueId=4478e39c wrap=true}
+```rust
+fn main() {}
+```
+:::
+
+:::codeBlock {language="a\u0060b"}
+```
+x
+```
+:::
+
+:::codeBlock {language=" sql"}
+```
+SELECT 1
+```
+:::
+
+:::codeBlock {language="\u0026#97;df"}
+```
+y
+```
+:::