Adjust elevation check for net host

[YuliiaKovalova]

Fixes #12385

Context

MSBuild handshake failures occur when an elevated MSBuild.exe process (running on .NET Framework) attempts to communicate with dotnet.exe child processes (running on .NET). The issue stems from a platform compatibility problem where:

• MSBuild.exe includes HandshakeOptions.Administrator flag when running elevated (due to FEATURE_SECURITY_PRINCIPAL_WINDOWS being available)
• dotnet.exe child processes cannot include this flag because WindowsPrincipal/WindowsIdentity APIs are not available in modern .NET runtimes
• This creates a handshake mismatch even when both processes have identical elevation levels (High Integrity)

Changes Made

• Updated the elevation check in GetHandshakeOptions() to make elevation validation avaialble for .NET task host scenarios

Testing

• Tested handshake completion without elevation flag mismatches

[Copilot]

Pull Request Overview

This PR fixes a handshake failure between elevated MSBuild.exe processes (running on .NET Framework) and dotnet.exe child processes (running on .NET). The issue occurs because MSBuild.exe can check for administrator privileges using Windows APIs that are unavailable in modern .NET runtimes, causing handshake mismatches.

• Modified elevation check logic to skip administrator privilege validation for .NET task host scenarios
• Added conditional guard to prevent HandshakeOptions.Administrator flag when communicating with .NET endpoints
• Maintains security intent while resolving cross-platform compatibility issues