Support web extension

[jetersen]

Consider adding support for github.dev and vscode.dev:

https://code.visualstudio.com/api/extension-guides/web-extensions

• I have a question that is specific to this extension; thus, inappropriate for the main EditorConfig issue tracker.

[andymac4182]

This would be great! I just tried to use this extension in github.dev :(

[megla-tlanghorst]

Same for the GitLab Web IDE, which is built on the VSCode for web source as well. It uses the extension via open-vsx (because Microsoft restrictions and stuff... coder, vscodium and gitpod also use it), but that just seems to mirror the VS marketplace.