[X] Fix XamlCompilation of RD subclasses

[StephaneDelcroix]

Description of Change

Fix an issue when compiling a non-direct descendant of RD

Issues Fixed

• fixes Getting AccessViolationException while adding custom resource dictionary in App.Xaml file in Release builds #19535

[rmarinho]

weird failure..

D:\a\_work\1\s\bin\dotnet\sdk\8.0.100\Microsoft.Common.CurrentVersion.targets(2146,5): warning : The referenced project '..\..\..\Controls\src\Core\Controls.SourceGen.csproj' does not exist. [D:\a\_work\1\s\src\Controls\samples\Controls.Sample\Maui.Controls.Sample.csproj::TargetFramework=net8.0-android]
D:\a\_work\1\s\bin\dotnet\sdk\8.0.100\Microsoft.Common.CurrentVersion.targets(2146,5): warning : The referenced project '..\..\..\Controls\src\Core\Controls.SourceGen.csproj' does not exist. [D:\a\_work\1\s\src\Controls\samples\Controls.Sample\Maui.Controls.Sample.csproj::TargetFramework=net8.0-android]
D:\a\_work\1\s\bin\dotnet\sdk\8.0.100\Microsoft.Common.CurrentVersion.targets(2146,5): warning : The referenced project '..\..\..\Controls\src\Core\Controls.SourceGen.csproj' does not exist. [D:\a\_work\1\s\src\Controls\samples\Controls.Sample\Maui.Controls.Sample.csproj::TargetFramework=net8.0-android]
D:\a\_work\1\s\bin\dotnet\sdk\8.0.100\Microsoft.Common.CurrentVersion.targets(2146,5): warning : The referenced project '..\..\..\Controls\src\Core\Controls.SourceGen.csproj' does not exist. [D:\a\_work\1\s\src\Controls\samples\Controls.Sample\Maui.Controls.Sample.csproj::TargetFramework=net8.0-android]
D:\a\_work\1\s\src\Maui.InTree.props(7,5): error MSB4024: The imported project file "D:\a\_work\1\s\.buildtasks\Microsoft.Maui.Core.props" could not be loaded. The process cannot access the file 'D:\a\_work\1\s\.buildtasks\Microsoft.Maui.Core.props' because it is being used by another process. [D:\a\_work\1\s\src\TestUtils\src\DeviceTests\TestUtils.DeviceTests.csproj]
    5844 Warning(s)
    1 Error(s)

[StephaneDelcroix]

@rmarinho looks unrelated