Add `FromIterator` implementations for `Cow<str>`
Add `FromIterator` implementations for `Cow<str>`

This seems like an oversight, since the corresponding implementation for `Cow<[T]> where T: Clone` exists.

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