Rollup merge of #77560 - rschoon:fix-litkind-rc-bytebuf, r=lcnr
Rollup merge of #77560 - rschoon:fix-litkind-rc-bytebuf, r=lcnr

Fix LitKind's byte buffer to use refcounted slice

While working on adding a new lint for clippy (see https://github.com/rust-lang/rust-clippy/pull/6044) for avoiding shared ownership of "mutable buffer" types (such as using `Rc<Vec<T>>` instead of `Rc<[T]>`), I noticed a type exported from rustc_ast and used by clippy gets caught by the lint. This PR fixes the exported type.

This PR includes the actual change to clippy too, but I will open a PR directly against clippy for that part (although it will currently fail to build there).

aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust