Split core/str/mod.rs to smaller files

[tesuji]

Note for reviewer:

• I split to multiple commits for easier reviewing, but I could git squash them all to one if requested.
• Recommend pulling this change locally and using advanced git diff viewer or this command:

  git show --reverse --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space master..

---

I split core/str/mod.rs to these modules:

• converts: Contains helper functions to convert from bytes to str.
• error: For error structs like Utf8Error.
• iter: For iterators of many str methods.
• traits: For indexing operations and build in traits on str.
• validations: For functions validating utf8 --- This name is awkward, maybe utf8.rs is better.

[tesuji]

@rustbot modify labels: +S-waiting-on-review

[jonas-schievink]

r? @KodrAus

[bors]

☔ The latest upstream changes (presumably #76964) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[tesuji]

Rebased.

[bors]

☔ The latest upstream changes (presumably #77201) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[tesuji]

Rebased.

[varkor]

@rust-lang/libs: is there someone who could review this PR? It bitrots quite quickly.

@bors p=100

[Amanieu]

@bors r+

Also I learned something new about git today!

[bors]

📌 Commit dce7248 has been approved by Amanieu

[bors]

⌛ Testing commit dce7248 with merge 9bb55dc...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: Amanieu
Pushing 9bb55dc to master...

[bjorn3]

This caused a 26.6% reduction on clap-rs-debug incr-patched: println. https://perf.rust-lang.org/compare.html?start=ef663a8a48ea6b98b43cbfaefd99316b36b16825&end=9bb55dc8642d811d66a7599812009cc063577e00&stat=instructions:u

[tesuji]

It also regresses wall-time and some max-rss tests: https://perf.rust-lang.org/compare.html?start=ef663a8a48ea6b98b43cbfaefd99316b36b16825&end=9bb55dc8642d811d66a7599812009cc063577e00&stat=wall-time

I don't think we could do anything to improve it.

[SimonSapin]

@bjorn3 Is that number really due to this PR? It looks like that benchmark has been oscillating between two results, recently:

[bjorn3]

Ah, ok.

[nervenes]

i think this was supposed to be type Error, is it possible to change this?

[sfackler]

You are 9.5 years too late to change this.

[bjorn3]

To elaborate: It was already type Err before this PR. #21718 which stabilized FromStr introduced type Err.