Code-gen shouldDispose ctor and Dispose pattern

[krwq]

Almost all device bindings have _i2cDevice, _spiDevice and very similar Dispose code. Some of them provide shouldDispose flag. My suggestion is that we automate this part where possible:

• we create source generator (new roslyn feature)
• we remove explicit shouldDispose handling and replace that with generated code

for example

[GenerateDisposePattern] // whatever name, not much important
public partial class SomeDevice : IDisposable
{
  public SomeDevice(I2cDevice device, <some-other-args-but-nothing-related-to-disposing>)
  {
     //...
  }
}

generated code:

public partial class SomeDevice : IDisposable
{
  private bool _shouldDispose = true; // default based on majority of current implementation
  public SomeDevice(I2cDevice device, <some-other-args-but-nothing-related-to-disposing>, bool shouldDispose)
    : this(device, ....)
  {
    _shouldDispose = shouldDispose;
  }

  public void Dispose()
  {
     if (_shouldDispose)
     {
        // proper implementation, we pick member of type `I2cDevice`, `SpiDevice` etc
     }
  }
}

Related issues:

• Dispose not handled correctly #1272
• Reconsider Dispose pattern across devices #419
• and related section: https://github.com/dotnet/iot/blob/main/Documentation/Devices-conventions.md#lifetime-management-or-what-should-be-disposed-by-what (this should be checked if it's true - we should default to whatever is already in the code)

[joperezr]

Agreed, this would be cool. Perhaps we should also have a source generator for automatically taking in GpioController when appropriate and automatically taking GpioPin list.