Merge #252

252: Improve 'introduce variable' r=matklad a=flodiebold

 - make it possible to extract a prefix of an expression statement (e.g.
   `<|>foo.bar()<|>.baz()`)
 - don't turn the last expression in a block into a let statement
 - also fix a few typos

Co-authored-by: Florian Diebold <flodiebold@gmail.com>

diff --cc crates/ra_editor/src/code_actions.rs
Simple merge