PrinterSettings.SupportsColor property is broken

[Documentation](https://docs.microsoft.com/en-us/dotnet/api/system.drawing.printing.printersettings.supportscolor?view=netframework-4.8) claims that `SupportsColor` property :

> Gets a value indicating whether this printer supports color printing.

This is not accurate. This [property](https://github.com/dotnet/runtime/blob/1cf033de96a38b286c07b8311edd5f2eabcfb462/src/libraries/System.Drawing.Common/src/System/Drawing/Printing/PrinterSettings.Windows.cs#L516-L522) P/Invokes [GetDeviceCaps(BITSPIXEL..)](https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getdevicecaps), which returns:

> Number of adjacent color bits for each pixel.

It does not take into account "color planes" or gray-scale rendering. I would not recommend using this API in .NET Framework. However in .NET Core 5, we fixed it(issue #34630). I think we should publish a workaround in the docs:

```
using System;
using System.Drawing.Printing;
using System.Runtime.InteropServices;

namespace ConsoleApp1
{
class Program
{
static void Main(string[] _)
{
PrinterSettingsTest();
}

static void PrinterSettingsTest()
{
var document = new PrintDocument();
foreach (string name in PrinterSettings.InstalledPrinters)
{
document.PrinterSettings.PrinterName = name;
Console.WriteLine($"{name} SupportsColor = {document.PrinterSettings.SupportsColor}");
var capability = GetColorDeviceCapability(name);
Console.WriteLine($"\tDeviceCapabilities(DC_COLORDEVICE) returns {capability}");
}

Console.ReadLine();
}

[DllImport("winspool.drv", SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true)]
private static extern int DeviceCapabilitiesW(string pDevice, string pPort, short fwCapabilities, IntPtr pOutput, IntPtr pDevMode);
private const short DC_COLORDEVICE = 32;

private static bool GetColorDeviceCapability(string printerName)
{
return DeviceCapabilitiesW(printerName, null, DC_COLORDEVICE, IntPtr.Zero, IntPtr.Zero) == 1;
}
}
}
```

Start with the PrinterSettings.SupportsColor API documentation linked in the issue, then compare its description with PrinterSettings.Windows.cs and the referenced GetDeviceCaps behavior. Document the .NET Framework limitation and the supplied DeviceCapabilitiesW workaround, with the page clearly distinguishing the corrected .NET Core 5 behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.