HardwareSerial:begin() changes RTS and CTS pins preventing detaching those pins

[SuGlider]

Description of Change

Begin() may "undo" a setpins() that has set RTS and/or CTS pin.
As consequence, RTS and CTS won't be detached with end().
This pins are only changed by using setPins() passing RTS and CTS.

setpins() can be called after or before begin()
when called before, begin() shall not change those pins.

This PR fixes it.

Tests scenarios

Tested with ESP32 just checking logs.

void setup() {
  Serial.setPins(3, 1, 25, 26); // ESP32 RX, TX, CTS, RTS
  Serial.begin(115200);
  Serial.end();  // only detaches RX and TX. CTS and RTS will be -1 after begin() and won't be detached!
}
void loop() {}

Related links

This changes has been backported to 2.0.15 by #9176

[github-actions]

	Warnings
⚠️	Some issues found for the commit messages in this PR: the commit message "fix: begin cts rts": summary looks too short Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).
⚠️	The source branch "SuGlider-patch-1" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

👋 Hello SuGlider, we appreciate your contribution to this project!

---

Click to see more instructions ...

This automated output is generated by the PR linter DangerJS, which checks if your Pull Request meets the project's requirements and helps you fix potential issues.

DangerJS is triggered with each push event to a Pull Request and modify the contents of this comment.

Please consider the following:
- Danger mainly focuses on the PR structure and formatting and can't understand the meaning behind your code or changes.
- Danger is not a substitute for human code reviews; it's still important to request a code review from your colleagues.
- Resolve all warnings (⚠️ ) before requesting a review from human reviewers - they will appreciate it.
- To manually retry these Danger checks, please navigate to the Actions tab and re-run last Danger workflow.

Review and merge process you can expect ...

We do welcome contributions in the form of bug reports, feature requests and pull requests.

1. An internal issue has been created for the PR, we assign it to the relevant engineer.
2. They review the PR and either approve it or ask you for changes or clarifications.
3. Once the GitHub PR is approved we do the final review, collect approvals from core owners and make sure all the automated tests are passing.
- At this point we may do some adjustments to the proposed change, or extend it by adding tests or documentation.
4. If the change is approved and passes the tests it is merged into the default branch.

Generated by 🚫 dangerJS against a488384