rustc-ap-syntax 67.0.0

Automatically published version of the package `syntax` in the rust-lang/rust repository from commit 521d91c6be76367d966df419677dd187f799b116
NB: This crate is part of the Rust compiler. For an overview of the
compiler as a whole, see
[the README.md file found in `librustc`](../librustc/README.md).

The `syntax` crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.