Rollup merge of rust-lang#105824 - zacchiro:patch-1, r=JohnTitor

str.lines() docstring: clarify that line endings are not returned

Previously, the str.lines() docstring stated that lines are split at line endings, but not whether those were returned or not.  This new version of the docstring states this explicitly, avoiding the need of getting to doctests to get an answer to this FAQ.

Author: Yuki Okushi