Adding attributes to fenced markdown code blocks breaks syntax highlighting

[janosh]

The following highlights fine in VS Code markdown.

```py
def greetings():
    print("Hello world!")
```

If I add attributes like line highlighting or a title, syntax highlighting is gone.

```py{1}:title=greet.py
def greetings():
    print("Hello world!")
```

How about just discarding everything after the first special character when reading the fence's language specifier?

[mjbvz]

What markdown engine uses that syntax?

[janosh]

@mjbvz Not part of an engine. It's preprocessing but the practice of adding various attributes to code fences is quite wide spread. In my case, the titles are powered by gatsby-remark-code-titles and the line lighlighting by gatsby-remark-vscode

[mjbvz]

Ok, I asked because we do already ignore attribute but other parsers require a space between the language name and attributes

PRs welcome but keep in mind that some language names do contain special characters (c++, c#, ...). You likely need to change this line and add tests:

vscode-markdown-tm-grammar/build.js

Line 83 in b6d7f71

(^|\\G)(\\s*)(\`{3,}|~{3,})\\s*(?i:(${identifiers.join('|')})(\\s+[^\`~]*)?$)