Don't remove color information from rendered string in --message-format=json output

[mchernyavsky]

Describe the problem you are trying to solve

I'm trying to support new build tool window for IntelliJ Rust:

I use --message-format=json option, but unfortunately the rendered string doesn't contain color information.

Describe the solution you'd like

I would like to use --color=always option (or some new one) to include color information.

Notes
I think this is the place where it can be fixed:

cargo/src/cargo/core/compiler/mod.rs

Lines 1222 to 1238 in 9be4594

	// Remove color information from the rendered string. rustc has not
	// included color in the past, so to avoid breaking anything, strip it
	// out when --json-rendered=termcolor is used. This runs
	// unconditionally under the assumption that Cargo will eventually
	// move to this as the default mode. Perhaps in the future, cargo
	// could allow the user to enable/disable color (such as with a
	// `--json-rendered` or `--color` or `--message-format` flag).
	#[derive(serde::Deserialize, serde::Serialize)]
	struct CompilerMessage {
	rendered: String,
	#[serde(flatten)]
	other: std::collections::BTreeMap<String, serde_json::Value>,
	}
	if let Ok(mut error) = serde_json::from_str::<CompilerMessage>(compiler_message.get()) {
	error.rendered = strip_ansi_escapes::strip(&error.rendered)
	.map(|v| String::from_utf8(v).expect("utf8"))
	.unwrap_or(error.rendered);

[ehuss]

This is gated on rust-lang/rust#60987

[mchernyavsky]

Thanks!