Rollup merge of #56255 - jasonl:update-old-documents, r=michaelwoerister
Rollup merge of #56255 - jasonl:update-old-documents, r=michaelwoerister

Update outdated code comments in StringReader

For the detection of newlines in the lexer, this is now done in `analyze_source_file.rs`.

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