Added example to demonstrate using HardwareSerial with RS485 interfaces

[econeale]

Description of Change

This PR adds an example to the set of Serial examples that demonstrates how to use the HardwareSerial interface to communicate using RS485 hardware. The demo simply echos data received on one interface to the other.

Tests scenarios

I have tested with Adafruit Huzzah32 (ESP32) and Adafruit QT Py ESP32-S3 using a MAX33046E translation chip.

Related links

Addendum to #8934
Potentially related to #8755

[CLAassistant]

All committers have signed the CLA.

[lucasssvaz]

You can also remove this as it is already included by default.

[VojtechBartoska]

Hi @econeale, can you please update your PR up to the reviews? Thanks a lot!

[github-actions]

	Warnings
⚠️	Some issues found for the commit messages in this PR: the commit message "Added Serial as RS485 interface demo": summary looks empty type/action looks empty the commit message "Added more detail to initial comment": summary looks empty type/action looks empty the commit message "Removed HardwareSerial.h include. Switched RTS pin to GPIO 4 for broader compatability.": summary should not end with a period (full stop) summary looks empty type/action looks empty the commit message "Switched to UART_MODE definitions from uart_types.h in order to accomodate some versions of Arduino core": summary looks empty type/action looks empty the commit message "Update libraries/ESP32/examples/Serial/RS485_Echo_Demo/RS485_Echo_Demo.ino": summary looks empty type/action looks empty the commit message "Update libraries/ESP32/examples/Serial/RS485_Echo_Demo/RS485_Echo_Demo.ino": summary looks empty type/action looks empty the commit message "Update libraries/ESP32/examples/Serial/RS485_Echo_Demo/RS485_Echo_Demo.ino": summary looks empty type/action looks empty the commit message "using 115200 for UART0 - console": summary looks empty type/action looks empty 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 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).
⚠️	Please consider squashing your 10 commits (simplifying branch history).

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

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[SuGlider]

@me-no-dev - this PR can also be merged.