Github flavored markdown

Like many developers, I primarily use VSCode to work on projects hosted on GitHub.

GitHub uses a custom markdown flavor, which adds several syntax features to markdown that have also been adopted (partially or in full) by other popular markdown renderers.

It would be nice to have a VSCode config to enable gfm, so that this;

```md
> [!note]
> something relevant
```

appears in the preview like this;

> [!note]
> something relevant

instead of like this;

> \[!note] something relevant

And other such gfm features are also rendered as they would be on GitHub rather than as they would be by a generic common mark implementation.

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QoL enhancement from this; if a git repo pointing to github is detected, either automatically enable the gfm feature, or prompt the user via toast to enable the feature themselves if it is not already enabled.

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Related;

#245064 was closed because VSCode only supports common mark - common mark does not support callouts, therefore VSCode does not support callouts. This is not a request to add callouts/other gfm to the existing markdown rendering pipeline, this is a request to add an option to swap out common mark for gfm, or to otherwise enable gfm based on user preference.

Start with VS Code's Markdown preview rendering pipeline and its current CommonMark implementation. Review how preview configuration is exposed, then verify the [!note] example and other GitHub-flavored syntax against GitHub's rendering. Done means an opt-in GFM mode renders the syntax correctly while preserving the existing default behavior; repository detection and prompting are optional enhancements described in the issue.

Written by the indexing model from the issue text.