FIX: DPI inconsistency of draggable legend #10469
Fix for #10458 : draggable legend has an inconsistent offset behavior between the DPI value used for display and the DPI value used for saving. This was introduced in 199a87a due to some refactoring that was just a bit too eager. This PR simply reverts the one line that is causing the issue, and fixes some typos in a related docstring. Please see #10458 for more details about the issue (bisect, manual test script, etc.).
As the side remark, this issue was silently introduced because it affects an interactive part of Matplotlib, thus that it is not exercised by the test suite (if I a remember correctly).