Rollup merge of #145568 - fee1-dead-contrib:push-uvsonuzxmkus, r=fmease

ignore frontmatters in `TokenStream::new`

Fixes rust-lang/rust#145520 for now, we'd likely want to figure the stripping part later, so I noted it down on the list on the tracking issue.

cc `@fmease`

Author: jieyouxu