Remove overlap between manual_split_once and needless_splitn

[Alexendoo]

changelog: Remove overlap between [manual_split_once] and [needless_splitn]. Fixes some incorrect rsplitn suggestions for [manual_split_once]

Things that can trigger needless_splitn no longer trigger manual_split_once, e.g.

s.[r]splitn(2, '=').next();
s.[r]splitn(2, '=').nth(0);
s.[r]splitn(3, '=').next_tuple();

Fixes some suggestions:

let s = "should not match";

s.rsplitn(2, '.').nth(1);
// old -> Some("should not match")
Some(s.rsplit_once('.').map_or(s, |x| x.0));
// new -> None
s.rsplit_once('.').map(|x| x.0);

s.rsplitn(2, '.').nth(1)?;
// old -> "should not match"
s.rsplit_once('.').map_or(s, |x| x.0);
// new -> early returns
s.rsplit_once('.')?.0;

[rust-highfive]

r? @xFrednet

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[xFrednet]

Overall looks good to me, a solid improvement and nice refactoring! Just one small NIT and then it's ready to be merged. 👍

And thank you for your patience, while waiting for a review. I appreciate it! 🙃

[xFrednet]

Looks good to me, thank you very much for the update 🙃

@bors r+

[bors]

📌 Commit 6fba897 has been approved by xFrednet

[bors]

⌛ Testing commit 6fba897 with merge 5344236...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing 5344236 to master...