Improvements device discovery and PortBase classes

[josesimoes]

Description

• Improve check of nanoBooter on device discovery: the code now checks for a valid marker in the received packet.
• PortBase class now has methods to Start and stop the device watchers and also to rescan devices.
• SerialPort and UsbPort now have an overloaded constructor allowing to instanciate the class without starting the device watchers.
• Update test app.

Motivation and Context

• Improves device discovery.
• Improves developer experience allowing VS to start debugger component with or without device watchers started.
• Improves developer experience allowing VS to rescan devices without forcing developer to physically unplug and plug nanoDevices that are behind a serial converter.

How Has This Been Tested?

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Signed-off-by: José Simões jose.simoes@eclo.solutions

[nfbot]

Hi @josesimoes,

I'm nanoFramework bot.
Thank you for your contribution!

A human will be reviewing it shortly. 😉