Build should validate solution root components and fail if any are missing

[zdeneksrejber]

Problem

The dotnet build process does not validate solution manifest completeness. Developers can remove root component entries from Solution.xml without build failure, leading to incomplete solutions that only fail during pack/import phases.

Current Behavior

Build command

dotnet build "Project.slnx"  # Exit code: 0 (PASS)

Example output

Feedback, Suggestions, Issues: https://github.com/microsoft/powerplatform-build-tools/discussions
  Error: RootComponent validation failed.
  Solution: bin\Debug\net462\Core.Features.WasteManagement.Composition.zip packed successfully
  Completed intermediate files clean up.

Build succeeded.

C:\Users\zdene\.nuget\packages\talxis.devkit.build.dataverse.tasks\1.2.2\tasks\Targets\GenerateVersionNumber.targets(10,3): warning : LocalBranchBuildVersionNumber is null, setting to default. [c:\Users\zdene\Sources\PCT21016\src\Modules.Core\Features.WasteManagement.Composition\Core.Features.WasteManagement.Composition.csproj]
    1 Warning(s)
    0 Error(s)

[TomProkop]

prereq: #43