feat: allow using filenames in codeblocks (#2455)

Allow using filenames in codeblocks

- If there is a dot in the language name, we instead treat the first line after ``` as the filename and everything after the last dot as the language
- we use a custom "data-label" attribute on the code block to specify the name of the file (so only compatible with cinny from this point onwards)

src/app/plugins/markdown/block/rules.ts

@@ -16,8 +16,12 @@ export const CodeBlockRule: BlockMDRule = {
   match: (text) => text.match(CODEBLOCK_REG_1),
   html: (match) => {
     const [, g1, g2] = match;
-    const classNameAtt = g1 ? ` class="language-${g1}"` : '';
-    return `<pre data-md="${CODEBLOCK_MD_1}"><code${classNameAtt}>${g2}</code></pre>`;
+    // use last identifier after dot, e.g. for "example.json" gets us "json" as language code.
+    const langCode = g1 ? g1.substring(g1.lastIndexOf('.') + 1) : null;
+    const filename = g1 != langCode ? g1 : null;
+    const classNameAtt = langCode ? ` class="language-${langCode}"` : '';
+    const filenameAtt = filename ? ` data-label="${filename}"` : '';
+    return `<pre data-md="${CODEBLOCK_MD_1}"><code${classNameAtt}${filenameAtt}>${g2}</code></pre>`;
   },
 };