Fix setting DPI awareness

[AustinWise]

Description

Currently DPI awareness will be enabled only if a DisableDpiAwarenessAttribute attribute is applied to the entry assembly. Which does not make a lot of sense. This also does not match the behavior of .NET 6.

This PR changes the logic to always enable DPI awareness unless a DisableDpiAwarenessAttribute attribute is applied to the entry assembly.

Customer Impact

WPF applications are not DPI aware. This can be seen by:

dotnet new wpf
dotnet run

And then checking the DPI Awareness column in Task Manager. On .NET 6 the DPI awareness is "System". In .NET 7 preview 1, it is "Unaware".

Regression

This regression was introduced by #5765, which migrated the DPI awareness enablement code from C++ to C#.

Testing

dotnet new wpf

Then replace the contents of MainWindow.xml.cs with:

using System.Windows;
using System.Runtime.InteropServices;

namespace test
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        [DllImport("User32", EntryPoint = "IsProcessDPIAware", CharSet = CharSet.Auto, SetLastError = true)]
        internal static extern bool IsProcessDPIAware();

        public MainWindow()
        {
            InitializeComponent();
            this.Title = IsProcessDPIAware().ToString();
        }
    }
}

Results of running this program on different versions of WPF:

.NET Version	title
6.0.3	True
7 Preview 1	False
This PR	True

Risk

Low.

[ThomasGoulet73]

Thank you! This is definitely a mistake on my part and I believe that this is the right fix.

[ThomasGoulet73]

Could you keep the comments at the same place as the previous C++ code? You can use this code for reference:

wpf/src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/main.cpp

Lines 184 to 205 in 560f243

	Assembly ^ assemblyApp;
	Type ^ disableDpiAwareType = System::Windows::Media::DisableDpiAwarenessAttribute::typeid;
	bool bDisableDpiAware = false;
	// By default, Application is DPIAware.
	assemblyApp = Assembly::GetEntryAssembly();
	// Check if the Application has explicitly set DisableDpiAwareness attribute.
	if (assemblyApp != nullptr && Attribute::IsDefined(assemblyApp, disableDpiAwareType))
	{
	bDisableDpiAware = true;
	}
	if (!bDisableDpiAware)
	{
	// DpiAware composition is enabled for this application.
	SetProcessDPIAware_Internal( );
	}
	// Only when DisableDpiAwareness attribute is set in Application assembly,
	// It will ignore the SetProcessDPIAware API call.

[AustinWise]

I changed it it to match the original C++ code more closely. I renamed bDisableDpiAware to disableDpiAware, so that it matches typical C# conventions.