No-newline indicator now visible in diffs; stash conflicts show descriptive error

Fixed

• Screen reader now correctly announces added and removed line counts in the pull request preview dialog - #22202

Improved

• Show "No newline at end of file" as visible text in the diff view instead of requiring a tooltip hover - #22204
• Show a descriptive error dialog when restoring stashed changes fails due to conflicting changes in the working directory - #22205