zerocopy-derive lost ability to parse raw identifiers in 0.8.13

[erickt]

zerocopy-derive used to support struct fields with raw identifiers, like r#type, up to 0.8.12, but this was broken in 0.8.13. For example:

use zerocopy::byteorder::network_endian::U16;
use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout, Unaligned};

#[repr(C)]
#[derive(KnownLayout, FromBytes, IntoBytes, Immutable, Unaligned, Debug, PartialEq, Eq, Clone)]
pub struct IcmpHeader {
    r#type: u8,
    code: u8,
    checksum: U16,
    id: U16,
    sequence: U16,
}

This compiles successfully with this Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[dependencies]
zerocopy = { version = "=0.8.12", features = ["derive"] }

But fails with this Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[dependencies]
zerocopy = { version = "=0.8.13", features = ["derive"] }

with this error message:

% cargo build
    Updating crates.io index
   Compiling foo v0.1.0 (/usr/local/google/home/etryzelaar/foo)
error: proc-macro derive panicked
 --> src/lib.rs:5:10
  |
5 | #[derive(KnownLayout, FromBytes, IntoBytes, Immutable, Unaligned, Debug, PartialEq, Eq, Clone)]
  |          ^^^^^^^^^^^
  |
  = help: message: `"__Zerocopy_Field_r#type"` is not a valid identifier