Fix invalid suppression in System.Attribute

The suppression on System.Attribute is wrong. Ran into this in dotnet#70201 where `EditorBrowsableAttributeTests.EqualsTest` is failing because we didn't generate any reflection metadata for the field.

There's a difference between "a field is kept" and "a field is accessible from reflection without issues". The issue is more pronounced in Native AOT (where the field can be completely erased from reflection). The implementation of Attribute.Equals didn't see any fields on the attribute type because the static analysis didn't deem any of them necessary.

This fixes the suppression and replaces it with a more correct DAM on type.

src/libraries/System.Private.CoreLib/src/System/Attribute.cs

@@ -10,12 +10,11 @@ namespace System
     [AttributeUsage(AttributeTargets.All, Inherited = true, AllowMultiple = false)]
     [Serializable]
     [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
+    [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.NonPublicFields | DynamicallyAccessedMemberTypes.PublicFields)]
     public abstract partial class Attribute
     {
         protected Attribute() { }
 
-        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2075:UnrecognizedReflectionPattern",
-            Justification = "Unused fields don't make a difference for equality")]
         public override bool Equals([NotNullWhen(true)] object? obj)
         {
             if (obj == null)
@@ -48,8 +47,6 @@ public override bool Equals([NotNullWhen(true)] object? obj)
             return true;
         }
 
-        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2075:UnrecognizedReflectionPattern",
-            Justification = "Unused fields don't make a difference for hashcode quality")]
         public override int GetHashCode()
         {
             Type type = GetType();

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -498,6 +498,7 @@ public AssemblyLoadEventArgs(System.Reflection.Assembly loadedAssembly) { }
     public delegate void AssemblyLoadEventHandler(object? sender, System.AssemblyLoadEventArgs args);
     public delegate void AsyncCallback(System.IAsyncResult ar);
     [System.AttributeUsageAttribute(System.AttributeTargets.All, Inherited=true, AllowMultiple=false)]
+    [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
     public abstract partial class Attribute
     {
         protected Attribute() { }