No editor newlines shown (UI improvement)

# Current behavior

- No editor newlines shown
- Users can be easily confused with having a newline when typing 'enter' and the preview does not show a newline

# Expected behavior

- Show if there is a newline character at the end of the line (optional on/off)

# Environment

- Boost Note.next version: 0.21.1
- OS version and name: All (Windows, macOS, Linux)