Since <rust-lang#121358>, `TypeId` is
represented as a `(u64, u64)`. This also made the debug implementation a
lot larger, which is especially apparent with pretty formatting.

Make this less noisy by converting the inner value back to a `u128` then
printing as a tuple struct.

Current:

    TypeId { t: (1403077013027291752, 4518903163082958039) }
    TypeId {
        t: (
            1403077013027291752,
            4518903163082958039,
        ),
    }

New:

    TypeId(25882202575019293479932656973818029271)
    TypeId(
        25882202575019293479932656973818029271,
    )

Updated docs on `#[panic_handler]` in `library/core/src/lib.rs`

…=Mark-Simulacrum

Add `.ignore` file to make `config.toml` searchable in vscode

Based on this answer on [Stack Overflow](https://stackoverflow.com/a/72059075).

… r=Mark-Simulacrum

Small fixme in core now that split_first has no codegen issues

rust-lang#109328 (comment)

BTW, I have a crate implementing exactly this kind of an iterator: https://github.com/GrigorenkoPV/head-tail-iter and I was wondering if it would be worthwhile to try and make an ACP for it to get it included in std (or maybe itertools). My only doubt is that it kinda incentives writing O(n^2) algorithms and is not the hard to replace with a `while let` loop (just as in this PR).

…acrum

CI: rename Rust for Linux CI job

The `rfl` name was not very [descriptive](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Testing.20Rust.20for.20Linux.20in.20our.20CI/near/447408854).

try-job: x86_64-rust-for-linux

…ler-errors

Remove unused `rustc_trait_selection` dependencies

Found using `cargo-machete`. The `bitflags` and `derivative` crates were added for the new trait solver, but weren't removed when the next trait solver code was uplifted to a separate crate.

Print `TypeId` as a `u128` for `Debug`

Since <rust-lang#121358>, `TypeId` is represented as a `(u64, u64)`. This also made the debug implementation a lot larger, which is especially apparent with pretty formatting.

Change this to convert the inner value back to a `u128` and then print as a tuple struct to make this less noisy.

Current:

    TypeId { t: (1403077013027291752, 4518903163082958039) }
    TypeId {
        t: (
            1403077013027291752,
            4518903163082958039,
        ),
    }

New:

    TypeId(25882202575019293479932656973818029271)
    TypeId(
        25882202575019293479932656973818029271,
    )