Leverage `AlsoUsableForAttribute` for more interoperable typedefs

[AArnott]

microsoft/win32metadata#251 was just merged which adds AlsoUsableForAttribute. Is that worth waiting for?

Originally posted by @jnm2 in #185 (comment)

Also to accept SafeHandle everywhere that accepts the base type struct (e.g. HGDIOBJ, as mentioned in #205).

[AArnott]

An interesting sanity check after this feature is implemented would be to see if this sample compiles without errors:

using System.Drawing;
using System.Runtime.InteropServices;
using Windows.Win32;
using Windows.Win32.Foundation;
using Windows.Win32.Graphics.Gdi;
using static Windows.Win32.PInvoke;

class Helper
{
    public Bitmap GetScreenCapture(HWND handle)
    {
        Bitmap bitmap;

        RECT region;
        GetWindowRect(handle, out region);

        HWND desktopWindowHandle = GetDesktopWindow();
        using SafeHandle windowDCHandle = GetWindowsDC_SafeHandle(desktopWindowHandle);
        using DeleteDCSafeHandle memoryDCHandle = CreateCompatibleDC(windowDCHandle);
        using DeleteObjectSafeHandle bitmapHandle = CreateCompatibleBitmap(windowDCHandle, region.right - region.left, region.bottom - region.top);
        HGDIOBJ bitmapOldHandle = SelectObject(memoryDCHandle, (HGDIOBJ)bitmapHandle.DangerousGetHandle());

        bool success = BitBlt(memoryDCHandle, 0, 0, region.right - region.left, region.bottom - region.top, windowDCHandle, region.left, region.top, ROP_CODE.SRCCOPY | ROP_CODE.CAPTUREBLT);

        try
        {
            bitmap = Image.FromHbitmap(bitmapHandle.DangerousGetHandle());
        }
        finally
        {
            SelectObject(memoryDCHandle, bitmapOldHandle);
        }

        return bitmap;
    }
}

NativeMethods.txt:

GetWindowRect
GetDesktopWindow
GetWindowDC
CreateCompatibleDC
CreateCompatibleBitmap
SelectObject
BitBlt

Thanks to dotnet/pinvoke#593 who provided the basis for this sample.

[AArnott]

See also #491 which may make sense to fix at the same time as this one.

[AArnott]

Reopening so I can review all the notes here to ensure everything is truly resolved.