fix: updates public API surface with net8 target

Author: baywet

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -1,7 +1,7 @@
 [assembly: System.Reflection.AssemblyMetadata("RepositoryUrl", "https://github.com/Microsoft/OpenAPI.NET")]
 [assembly: System.Runtime.CompilerServices.InternalsVisibleTo(@"Microsoft.OpenApi.Readers.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100957cb48387b2a5f54f5ce39255f18f26d32a39990db27cf48737afc6bc62759ba996b8a2bfb675d4e39f3d06ecb55a178b1b4031dcb2a767e29977d88cce864a0d16bfc1b3bebb0edf9fe285f10fffc0a85f93d664fa05af07faa3aad2e545182dbf787e3fd32b56aca95df1a3c4e75dec164a3f1a4c653d971b01ffc39eb3c4")]
 [assembly: System.Runtime.CompilerServices.InternalsVisibleTo(@"Microsoft.OpenApi.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100957cb48387b2a5f54f5ce39255f18f26d32a39990db27cf48737afc6bc62759ba996b8a2bfb675d4e39f3d06ecb55a178b1b4031dcb2a767e29977d88cce864a0d16bfc1b3bebb0edf9fe285f10fffc0a85f93d664fa05af07faa3aad2e545182dbf787e3fd32b56aca95df1a3c4e75dec164a3f1a4c653d971b01ffc39eb3c4")]
-[assembly: System.Runtime.Versioning.TargetFramework(".NETStandard,Version=v2.0", FrameworkDisplayName=".NET Standard 2.0")]
+[assembly: System.Runtime.Versioning.TargetFramework(".NETCoreApp,Version=v8.0", FrameworkDisplayName=".NET 8.0")]
 public static class IDiagnosticExtensions
 {
     public static void AddRange<T>(this System.Collections.Generic.ICollection<T> collection, System.Collections.Generic.IEnumerable<T> enumerable) { }
@@ -148,6 +148,7 @@ namespace Microsoft.OpenApi.Extensions
 {
     public static class EnumExtensions
     {
+        [System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessage("Trimming", "IL2075", Justification="Fields are never trimmed for enum types.")]
         public static T GetAttributeOfType<T>(this System.Enum enumValue)
             where T : System.Attribute { }
         public static string GetDisplayName(this System.Enum enumValue) { }
@@ -198,7 +199,7 @@ namespace Microsoft.OpenApi.Extensions
     }
     public static class StringExtensions
     {
-        public static T GetEnumFromDisplayName<T>(this string displayName) { }
+        public static T GetEnumFromDisplayName<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]  T>(this string displayName) { }
     }
 }
 namespace Microsoft.OpenApi.Interfaces