codespace-linux: add Deno

[mfulton26]

Relates to: Codespaces

I'd like for Deno to be installed by default on codespace-linux containers; it is being used for many TypeScript projects and requires no additional setup for TypeScript unlike Node which only supports JavaScript out of the box.

[mfulton26]

I just tried out the Node.js & TypeScript container in Codespaces and it gave me the option to add additional tools; maybe what I should really be asking for is:

1. this same "mix-in" support for codespace-linux
2. making Deno an additional tool that can be mixed into these images

[bamurtaugh]

Thanks for opening an issue!

Our team has been actively working on an updated plan for community contributions and this repo moving forward, which we've now outlined in this issue: #1589. This includes moving to new repos for images (https://github.com/devcontainers/images) and Features (https://github.com/devcontainers/features), and we anticipate to have a similar repo and process for templates/definitions.

This sounds like a great opportunity to create and self-publish a Deno Feature (guidance here). cc @joshspicer @samruddhikhandale for the Codespaces aspect as well.