Styling of links is wrong within the banner

[a-stewart]

Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version: 1.62.0-dev
• OS Version: Mac OS 12.1

Steps to Reproduce:

1. Create a banner which uses a link.

    this.bannerService.show({
      id: 'test_id',
      icon: CodiconUtil.bellDot,
      message: new MarkdownString('**Test Message** [link](http://test/)'),
    });

Even though BannerService accepts a MarkdownString, the styling of links does not work as expected.

Note, this does not effect links provided within actions, just links defined within the markdown.

[JacksonKearl]

codicon color could be tweaked but overall 👍