Fix MSBuildEventSource

[dfederm]

I'm seeing this exception:

System.TypeInitializationException: The type initializer for 'Microsoft.Build.Eventing.MSBuildEventSource' threw an exception.
---> System.MissingMethodException: Method not found: 'Void System.Diagnostics.Tracing.EventSource..ctor(System.String, System.Guid)'.
   at Microsoft.Build.Eventing.MSBuildEventSource..ctor()
   at Microsoft.Build.Eventing.MSBuildEventSource..ctor()
   at Microsoft.Build.Eventing.MSBuildEventSource..cctor()
   --- End of inner exception stack trace ---
   at Microsoft.Build.Graph.ProjectGraph.<>c__DisplayClass41_0.<.ctor>g__BeginMeasurement|1()
   at Microsoft.Build.Graph.ProjectGraph..ctor(IEnumerable`1 entryPoints, ProjectCollection projectCollection, ProjectInstanceFactoryFunc projectInstanceFactory, Int32 degreeOfParallelism, CancellationToken cancellationToken)
   at Microsoft.Build.Graph.ProjectGraph..ctor(IEnumerable`1 entryPoints, ProjectCollection projectCollection, ProjectInstanceFactoryFunc projectInstanceFactory)

In ILSpy I see Microsoft.Build.Framework.dll 18.3.0-preview-26055-101+e64f84d6312cdaf227d26aeabfa4817862404d59 having:

    private MSBuildEventSource()
        : base("Microsoft-Build", new Guid(3561627800u, 33311, 22536, 76, 234, 30, 36, 233, 130, 202, 55))
    {
    }

But in C:\Program Files\dotnet\shared\Microsoft.NETCore.App\10.0.1\System.Private.CoreLib.dll (loaded in .NET 10) I see:

internal EventSource(Guid eventSourceGuid, string eventSourceName)
    : this(eventSourceGuid, eventSourceName, EventSourceSettings.EtwManifestEventFormat)
{
}

It's both internal and the args are backwards...

I believe this was introduced in #12886.

Which pulls in this change: dotnet/runtime#121180

That seems to introduce a source generator which calls the internal ctor of EventSource (and with different order). As that's internal to .NET, I expect it was not intended to be applied here in MSBuild.

This change simply reverts the change to MSBuildEventSource.

[Copilot]

Pull request overview

This PR fixes a MissingMethodException in MSBuildEventSource that was introduced by a previous change (PR #12886) that attempted to use the .NET runtime's EventSource source generator. The source generator was calling an internal EventSource constructor that is not available in the public API, causing runtime failures when MSBuild is used with .NET 10.

Changes:

• Removed the partial keyword from MSBuildEventSource class declaration
• Added an explicit private parameterless constructor to restore the original functionality

[AR-May]

/azp run

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