Deno runtime support

[donmccurdy]

Continuing from #380 and #379, I intend to support Deno as an environment. The I/O class has been added, but a few remaining things to do:

• Unit test coverage: Add test scaffold for Deno #456
• CI: Add CI for Deno #836
• Publish to https://jsr.io/

Context:

• Deno support avajs/ava#2743

TypeScript's magic ./foo → ./foo.ts resolution is causing quite a headache here.

• Cannot resolve module without extension defined denoland/deno#2506
• Suppressing "The import path cannot end with a '.ts' extension" error? microsoft/TypeScript#27481
• allow voluntary .ts suffix for import paths microsoft/TypeScript#37582
• --moduleResolution bundler (formerly known as hybrid) microsoft/TypeScript#51669 (possible resolution?)

[rotu]

It seems like DenoIO.write doesn't exist and NodeIO works fine on deno. Maybe DenoIO isn't needed?

[donmccurdy]

I'm not caught up on the latest changes in Deno v2 yet, but I understand they've prioritized compatibility with the Node.js ecosystem, and I agree that a DenoIO class isn't strictly required. That said — I think I do prefer to keep it, even if it's just an empty subclass of NodeIO. Deno isn't Node.js, and I think deserves equal standing as an I/O class. It's possible we may want a slightly different implementation at some point, too.