Add HW DTR support (port of #2994)

[i404788]

Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
• My changes were added to the CHANGELOG.md in the proper section.
• I have added necessary changes to user code to the Migration Guide.
• My changes are in accordance to the esp-rs developer guidelines

Extra:

• I have read the CONTRIBUTING.md guide and followed its instructions.

Pull Request Details 📖

Description

This is a port of #2994 for mainline (1.0.0-beta1).

Testing

Currently test it on a board to control an RS485 transceiver chip

[bugadani]

It's somewhat unclear to me what we are supposed to do with ESP32 :/

[bugadani]

• needs to be unstable (if you keep it)
• should be called into_rs485 and there is no way to disable it, either (if you keep it).
• Maybe this function should be turned into a Config struct field? All other configuration is set there.
• I'm still not sure we want to shoehorn RS485 into the main UART driver. Given that this is pretty minor and also unstable, maybe we can, for now.

[MabezDev]

Maybe this function should be turned into a Config struct field? All other configuration is set there.

I don't know nearly enough about rs485, but I think I agree here. Especially when you think about how to turn it off. We already have options, like hardware flow control, which have a config setting and require pins to be passed. I think we should follow this pattern.

I'm still not sure we want to shoehorn RS485 into the main UART driver. Given that this is pretty minor and also unstable, maybe we can, for now.

I agree, that we can experiment with this as an unstable API and figure out if it needs to be a separate driver.

[bugadani]

Okay apparently DTR/DSR are not available in the hardware

[i404788]

All fair points, I'm currently still testing it out after porting #2994. I think putting it in the Uart driver makes sense given the reference manual, but I'm not against something like an Rs485<'a, T: Uart> but either way you need to access the Uart registers.

[github-actions]

New commits in main has made this PR unmergable. Please resolve the conflicts.