Apply code suggestions from Visual Studio (#34064)

Applies a number of Visual Studio suggestions and errors found while
working on #34063.

Author: martincostello

src/Http/Routing/src/ModelEndpointDataSource.cs

@@ -12,7 +12,7 @@ namespace Microsoft.AspNetCore.Routing
 {
     internal class ModelEndpointDataSource : EndpointDataSource
     {
-        private List<DefaultEndpointConventionBuilder> _endpointConventionBuilders;
+        private readonly List<DefaultEndpointConventionBuilder> _endpointConventionBuilders;
 
         public ModelEndpointDataSource()
         {

src/Mvc/Mvc.ApiExplorer/src/DefaultApiDescriptionProvider.cs

@@ -338,7 +338,7 @@ private ApiParameterRouteInfo CreateRouteInfo(TemplatePart routeParameter)
             };
         }
 
-        private IEnumerable<string?> GetHttpMethods(ControllerActionDescriptor action)
+        private static IEnumerable<string?> GetHttpMethods(ControllerActionDescriptor action)
         {
             if (action.ActionConstraints != null && action.ActionConstraints.Count > 0)
             {
@@ -350,7 +350,7 @@ private ApiParameterRouteInfo CreateRouteInfo(TemplatePart routeParameter)
             }
         }
 
-        private RouteTemplate? ParseTemplate(ControllerActionDescriptor action)
+        private static RouteTemplate? ParseTemplate(ControllerActionDescriptor action)
         {
             if (action.AttributeRouteInfo?.Template != null)
             {
@@ -445,7 +445,7 @@ internal static MediaTypeCollection GetDeclaredContentTypes(IReadOnlyList<IApiRe
             return contentTypes;
         }
 
-        private IApiRequestMetadataProvider[]? GetRequestMetadataAttributes(ControllerActionDescriptor action)
+        private static IApiRequestMetadataProvider[]? GetRequestMetadataAttributes(ControllerActionDescriptor action)
         {
             if (action.FilterDescriptors == null)
             {

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

@@ -322,7 +322,7 @@ private static ApiResponseType CreateDefaultApiResponseType(Type responseType)
         }
 
         private static EndpointModelMetadata CreateModelMetadata(Type type) =>
-            new EndpointModelMetadata(ModelMetadataIdentity.ForType(type));
+            new(ModelMetadataIdentity.ForType(type));
 
         private static void AddResponseContentTypes(IList<ApiResponseFormat> apiResponseFormats, IReadOnlyList<string> contentTypes)
         {

src/Mvc/Mvc.Core/src/Routing/ActionEndpointFactory.cs

@@ -304,7 +304,7 @@ private static (RoutePattern resolvedRoutePattern, IDictionary<string, string?>
             return (attributeRoutePattern, resolvedRequiredValues ?? action.RouteValues);
         }
 
-        private void AddActionDataToBuilder(
+        private static void AddActionDataToBuilder(
             EndpointBuilder builder,
             HashSet<string> routeNames,
             ActionDescriptor action,