Add new fields for internal test crate

[tamird]

Adjusting to changes made in:

• Do not panic when a test function returns Result::Err. rust-lang/rust#100451
• Implementing "<test_binary> --list --format json" for use by IDE test explorers / runners rust-lang/rust#108148

[tamird]

Hmm, I see a bunch of errors of the form

error: crate `rustc_session` required to be available in rlib format, but was not found in this form
  |
  = help: try adding `extern crate rustc_driver;` at the top level of this crate

Thoughts?

[Manishearth]

Unsure, we haven't been trying hard to keep the nightly-feature stuff working.

It's possible the rustc internal components are distributed separately now.

I'll still merge this since it's an improvement.