publish VS Code extension on extensions marketplace

[zygoloid]

We should publish our VS Code extension for Carbon on the VS Code marketplace. We'll need to figure out what steps we need to follow here for publishing it and keeping it up to date.

[RohanVashisht1234]

I am ready to contribute:
I can transfer the ownership of my GitHub repository to carbon-language so that there is a base on which we can build carbon syntax highlighter further.

[zygoloid]

@RohanVashisht1234 If you can send us a PR to extend https://github.com/carbon-language/carbon-lang/tree/trunk/utils/vscode with your changes, that'd be ideal. Note that we do require that contributions follow our license rather than GPLv3.

With the newest version of VS Code, we can now provide a direct recommendation for use of our extension from within our own repository, without putting the extension on the marketplace: #3951 -- but that only addresses our own internal needs, not those of people using Carbon in other repos.

[RohanVashisht1234]

Sure, I am making the PR