Improvements and fixes in SerialPort

[josesimoes]

Description

• Rework constructor.
• Remove default values from backing fields as they are being initialized in the constructor anyway.
• Reorganized fields.
• SerialPort object is now added to controller in constructor and is not removed from there until it's disposed (the key is the portId which is set in the constructor and can't be changed).
• Remove setter from PortName as we can't safely support changing UART "on the fly".
• Add check to properties and calling native config only if port is opened.
• Remove _hasBeenOpened and associated code.
• Add missing extern to BytesToRead property.
• Add debugger attributes to prevent inspection and change by debugger.
• Bump assembly native version.

Motivation and Context

• Fix potential issues with reassigning UART on the fly.
• Fix issue with serial port object being added and remove from the serial controller.
• Fix issue with BytesToRead property.
• Fixes System.IO.Port watchChar declaration causes exception Home#762.
• Resolves System.IO.Ports SerialPort raised an exception when added event handler before Open() method call. Home#776.

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)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (work on Unit Tests, has no impact on code or features)

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.

[Ellerbach]

Looks good to me, thanks for the rework!