[API Proposal]: Public the ScanCode property in KeyEventArgs

[lindexi]

Background and motivation

As unoplatform/uno#14371 (comment) , the UNO for WPF will use reflection to get the ScanCode property in KeyEventArgs.

And the ScanCode property in KeyEventArgs is useful in many businesses code or framework code.

This property is rarely used in WPF today.

The code to get the ScanCode (only ways) :

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/InterOp/HwndSource.cs

Line 2362 in 187be47

int scanCode = HwndKeyboardInputProvider.GetScanCode(msg.wParam, msg.lParam);

The code to use ScanCode (only ways) :

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/TextCompositionManager.cs

Line 435 in 187be47

if (HandleAltNumpadEntry(keyArgs.RealKey, keyArgs.ScanCode, keyArgs.IsExtendedKey))

API Proposal

public class KeyEventArgs
{
    public int ScanCode { get; internal set; }
}

Or

public class KeyEventArgs
{
    public int ScanCode { get; set; }
}

API Usage

KeyEventArgs args = ...;
var scanCode = args.ScanCode.

Alternative Designs

No response

Risks

No response

[miloush]

Few things:

1. Note that this is public on RawKeyboardInputReport. Also note that rather than reflection, people can use MapVirtualKey to get the SC from VK.
2. This should be public get only like the other properties on KeyEventArgs.
3. You need an information on the extended keys. A lazy option would be to make the IsExtendedKey public as well, but there is now MAPVK_VK_TO_VSC_EX which gives you the actual extended scancode. I would think that would be preferable.
4. I am not entirely convinced this should be exposed on KeyEventArgs, because it doesn't even expose virtual keys. Maybe an interop method similar to getting VK would be more consistent.

[lindexi]

Few things:

1. Note that this is public on `RawKeyboardInputReport`. Also note that rather than reflection, people can use MapVirtualKey to get the SC from VK.

2. This should be public get only like the other properties on `KeyEventArgs`.

3. You need an information on the extended keys. A lazy option would be to make the `IsExtendedKey` public as well, but there is now `MAPVK_VK_TO_VSC_EX` which gives you the actual extended scancode. I would think that would be preferable.

4. I am not entirely convinced this should be exposed on `KeyEventArgs`, because it doesn't even expose virtual keys. Maybe an interop method similar to getting VK would be more consistent.

For 1.

        var key = e.Key;
        var virtualKey = KeyInterop.VirtualKeyFromKey(key);

        // MAPVK_VK_TO_VSC 0
        var scanCode = MapVirtualKeyW((uint) virtualKey, 0);

        var scanCodeFromWpf = typeof(KeyEventArgs).GetProperty("ScanCode", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)!.GetValue(e);

        Debug.Assert(scanCode == (int) scanCodeFromWpf!);

    [DllImport("User32.dll")]
    private static extern uint MapVirtualKeyW(uint code, uint mapType);