Auto merge of #35064 - pthariensflame:feature/cow_str_from_iter, r=alexcrichton
Auto merge of #35064 - pthariensflame:feature/cow_str_from_iter, r=alexcrichton

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

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

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