Ensure we log exception text when an exception is given (#77008)

The formatter passed doesn't include it (despite that the exception is
passed to it) so we must append it ourselves.

src/Workspaces/MSBuild/Core/MSBuild/DiagnosticReporterLoggerProvider.cs

@@ -52,6 +52,10 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
             if (!string.IsNullOrEmpty(categoryName))
                 message = $"[{categoryName}] {message}";
 
+            // The standard formatters don't actually include the exception, so let's include it ourselves
+            if (exception is not null)
+                message += Environment.NewLine + exception.ToString();
+
             reporter.Report(new WorkspaceDiagnostic(kind, message));
         }
     }