Rename MethodOverloadTestExtensions to OverloadTestExtensions

Also resolves other PR feedback, an extra blank line and incorrect use
of an implicit type.

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

@@ -517,7 +517,7 @@ bool IsAllowedKind(SyntaxKind kind) =>
                             {
                                 if (methods.ContainsKey(lm.Name))
                                 {
-                                    var currentCount = methods[lm.Name];
+                                    int currentCount = methods[lm.Name];
                                     lm.UniqueName = $"{lm.Name}{currentCount}";
                                     methods[lm.Name] = currentCount + 1;
                                 }

src/libraries/Microsoft.Extensions.Logging.Abstractions/tests/Microsoft.Extensions.Logging.Generators.Tests/TestClasses/MethodOverloadTestExtensions.cs → src/libraries/Microsoft.Extensions.Logging.Abstractions/tests/Microsoft.Extensions.Logging.Generators.Tests/TestClasses/OverloadTestExtensions.cs

@@ -11,7 +11,6 @@ internal static partial class OverloadTestExtensions
         [LoggerMessage(EventId = 1, Level = LogLevel.Trace, Message = "M0{p0}")]
         public static partial void M0(ILogger logger, string p0);
 
-
         [LoggerMessage(EventId = 2, EventName = "M1Custom", Level = LogLevel.Trace, Message = "M1{p0}")]
         public static partial void M1(ILogger logger, int p0);