Add minimal tsc output format

[JoviDeCroock]

Summary

Adds an explicit --outputFormat minimal command-line option for tsgo diagnostics. The minimal reporter emits one diagnostic per line in the form:

path/to/file.ts:line:character: TS1234: message | chained message

This keeps the default output unchanged while giving tooling and agents a compact, stable format that is easier to parse and significantly cheaper to feed back into LLM context windows.

Motivation

AI coding agents frequently run tsc/tsgo and then include the compiler output in the next prompt. The existing pretty/default diagnostics are excellent for humans, but they include context, spacing, colors, and multi-line message chains that add a lot of tokens. A compact output format reduces token usage and makes repeated fix/test loops less noisy without taking away the current default human-facing experience.

As a future follow-up, we could also auto-select this format when tsgo is run by an agent. A similar principle is being explored in oxc by detecting agent-specific environment variables and switching to an agent-oriented output format: oxc-project/oxc#22068. That PR mirrors the environment detection used by unjs/std-env agents detection, which is also used by tools like Vitest.

[jakebailey]

You should be writing end-to-end tests in tsctests, not unit tests here (or elsehwere, really)

[JoviDeCroock]

Thank you for the feedback, very new to GO so appreciate you chiming in quickly here. The tests were generated ahead of time by an LLM so I had something sane to work against.

I explicitly left it in Draft for that reason so we could talk through the desire for this feature. I think it could be valuable in terms of working towards a future where we save tokens of diagnostics coming from testing/linting/...

[JoviDeCroock]

@microsoft-github-policy-service agree