WinUI 3 does not use the darker shadow for dark mode windows

[BreeceW]

Describe the bug

Apps in dark mode on Windows (UWP dark mode or Win32 apps that set DWMWA_USE_IMMERSIVE_DARK_MODE) get a larger shadow, which makes them more visible, as the shadow is harder to see in dark mode otherwise. WinUI 3 does not use this larger shadow in dark mode, so they have worse contrast when glancing at open windows.

Steps to reproduce the bug

Compare the shadows of a UWP app when the light/dark mode settings are changed in Windows Settings and observe that the shadow grows in dark mode.
Then, look at a WinUI 3 app and observe that the shadow stays the same.

Note: This all assumes that Window.ExtendsContentIntoTitleBar was not set to true. Setting that to true turns immersive dark mode on, even if the app is in light mode. That results in a shadow that is too dark for light mode. See #8377.

Expected behavior

In dark mode, the shadow should be bigger/darker.

Screenshots

It’s a little hard to see, but UWP/immersive in dark mode has a bolder, darker shadow than in light mode. WinUI 3 should use that darker shadow when dark mode is on.

NuGet package version

WinUI 3 - Windows App SDK 1.2.5: 1.2.230313.1

Windows version

Windows 11 (22H2): Build 22621

Additional context

This could be implemented by setting DWMWA_USE_IMMERSIVE_DARK_MODE to true when the WinUI 3 app is in dark mode.

A workaround for this problem exists and is rather easy:
Simply call DwmSetWindowAttribute(WindowNative.GetWindowHandle(this), DWMWA_USE_IMMERSIVE_DARK_MODE, ...) with true or false as the value depending on whether your app is in dark or light mode. Make sure to update it when theme changes occur.