Mark logging source generator file as generated (#53275)

Give the output file for the M.E.Logging logging classes a ".g" suffix
so that it is treated as a generated file to prevent it being flagged by
source analyzers for violations the application developer cannot fix
for themselves.

Author: martincostello

src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.cs

@@ -39,7 +39,7 @@ public void Execute(GeneratorExecutionContext context)
                 var e = new Emitter();
                 string result = e.Emit(logClasses, context.CancellationToken);
 
-                context.AddSource("LoggerMessage", SourceText.From(result, Encoding.UTF8));
+                context.AddSource("LoggerMessage.g.cs", SourceText.From(result, Encoding.UTF8));
             }
         }