Enable MA0057 and fix noncompliance

"Class name should end with 'Attribute'" (when subclassing `Attribute`)

.global.editorconfig.ini

@@ -213,7 +213,7 @@ dotnet_diagnostic.MA0055.severity = silent
 # Do not call overridable members in constructor
 dotnet_diagnostic.MA0056.severity = silent
 # Class name should end with 'Attribute'
-dotnet_diagnostic.MA0057.severity = silent
+dotnet_diagnostic.MA0057.severity = error
 # Class name should end with 'Exception'
 dotnet_diagnostic.MA0058.severity = error
 # Class name should end with 'EventArgs'

src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs

@@ -8,6 +8,7 @@ using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
 {
+#pragma warning disable MA0057 // oops, should have called these `*Attribute`, too late now --yoshi
 	public static class ExternalToolApplicability
 	{
 		/// <remarks>This class is not deprecated, do not remove it.</remarks>
@@ -100,6 +101,7 @@ namespace BizHawk.Client.Common
 
 		public class DuplicateException : Exception {}
 	}
+#pragma warning disable MA0057
 
 	[AttributeUsage(AttributeTargets.Class)]
 	public sealed class ExternalToolAttribute : Attribute

src/BizHawk.Emulation.Common/Interfaces/Services/ISettable.cs

@@ -60,9 +60,7 @@ namespace BizHawk.Emulation.Common
 	/// Classes with this attribute will have a BizHawk.Common.SettingsUtil.SetDefaultValues(T) function generated
 	/// </summary>
 	[AttributeUsage(AttributeTargets.Class)]
-	public class CoreSettings : Attribute
-	{
-	}
+	public class CoreSettingsAttribute : Attribute {}
 
 	//note: this is a bit of a frail API. If a frontend wants a new flag, cores won't know to yea or nay it
 	//this could be solved by adding a KnownSettingsDirtyBits on the settings interface