Bump Avalonia and Avalonia.Desktop

Bumps Avalonia from 11.3.16 to 12.0.3
Bumps Avalonia.Desktop from 11.3.16 to 12.0.3

---
updated-dependencies:
- dependency-name: Avalonia
  dependency-version: 12.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: Avalonia.Desktop
  dependency-version: 12.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Directory.Packages.props

@@ -16,8 +16,8 @@
     <PackageVersion Include="Microsoft.Win32.SystemEvents" Version="8.0.0" />
 
     <!-- Avalonia (Plan A: WPF -> Avalonia cutover). Track the latest 11.x stable. -->
-    <PackageVersion Include="Avalonia" Version="11.3.16" />
-    <PackageVersion Include="Avalonia.Desktop" Version="11.3.16" />
+    <PackageVersion Include="Avalonia" Version="12.0.3" />
+    <PackageVersion Include="Avalonia.Desktop" Version="12.0.3" />
     <PackageVersion Include="Avalonia.Themes.Fluent" Version="11.3.16" />
     <PackageVersion Include="Avalonia.Fonts.Inter" Version="11.3.16" />
     <PackageVersion Include="Avalonia.Markup.Xaml.Loader" Version="11.3.16" />