feat: support code block title

[bluwy]

Description

Supports title in code blocks:

```js [filename.js]
// ...
```

The title bar design is based on the code group tabs design. Previously, support for this syntax is indirectly added by https://github.com/yuyinws/vitepress-plugin-group-icons, so I had to make sure the changes I make can still somewhat work with the plugin, however I need to patch it slightly to prevent double title bars added by us and them.

cc @yuyinws the plugin might need a new option to disable its own [title] support if this PR is merged. I couldn't figure out an automatic way for the plugin to detect this feature.

Linked Issues

fixes #3746

Additional Context

I've skipped support for title bar support for code snippets as there's no syntax to disable it at the moment. The snippets extensions always adds a title, causing it to be shown expectedly, e.g. the CLI output docs here may show init.ansi as the title.

[bluwy]

src here is added by snippet.ts, however I think it's better if it's token.meta.src instead similar to how githubAlerts.ts uses it. But I didn't change it here as I don't want to accidentally break downstream if they use this internal info.

[yuyinws]

What if we migrate vitepress-plugin-group-icons to Vitepress as a built-in feature?

After this, all projects that used this plugin can safely remove it after upgrading to the latest version of Vitepress.

I'm happy to work for this.

cc @brc-dd

[bluwy]

I think in a way this PR is already a partial migrate to make the title work, and is better to implement this single feature first, then we can decide to implement icon support on top.

[pkg-pr-new]

npm i https://pkg.pr.new/vitepress@5007

commit: dda3756