rustdoc: properly calculate line length for impl where clauses
rustdoc: properly calculate line length for impl where clauses

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