fix(derive): split paragraphs on lines ending with double space or backslash

[JohanVonElectrum]

closes #5802

[epage]

In our contributor documentation, we ask for Issues before PRs, see https://github.com/clap-rs/clap/blob/master/CONTRIBUTING.md#where-to-start

This isn't just a prefunctory task but to make sure we are aligned on the problem and the solution before putting in effort into a PR and to make sure there is capacity for reviewing your PR. In fact, This PR does little to explain what it is doing. We also have had solution discussions in #2389. I'd recommend proposing your idea in #2389 before we move forward with a solution and as such I'm closing this for now to keep the focus on #2389.

[JohanVonElectrum]

Thank you for the clarification and feedback. I initially created this fix for personal use and shared it as a potential solution. Before submitting, I searched for issues related to newlines but didn’t come across #2389, as it focuses on general markdown parsing. I’ll follow the discussions there and contribute under that umbrella moving forward. I’ll continue using my fork in the meantime. Thanks again!