Make Enum.GetValues AOT-safe

...at the cost of a small compat break. We return `int[]` instead of `SomeInt32Enum[]`.

Fixes dotnet#72140.

We can also delete intrinsic handling of `Enum.GetValues` in dataflow analysis but I don't want to conflict with Vitek's dotnet#71485.

src/coreclr/nativeaot/System.Private.CoreLib/src/System/RuntimeType.cs

@@ -91,24 +91,14 @@ public sealed override bool IsEnumDefined(object value)
             }
         }
 
-        [RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload instead.")]
         public sealed override Array GetEnumValues()
         {
             if (!IsActualEnum)
                 throw new ArgumentException(SR.Arg_MustBeEnum, "enumType");
 
-            Array values = Enum.GetEnumInfo(this).ValuesAsUnderlyingType;
-            int count = values.Length;
-            // Without universal shared generics, chances are slim that we'll have the appropriate
-            // array type available. Offer an escape hatch that avoids a MissingMetadataException
-            // at the cost of a small appcompat risk.
-            Array result;
-            if (AppContext.TryGetSwitch("Switch.System.Enum.RelaxedGetValues", out bool isRelaxed) && isRelaxed)
-                result = Array.CreateInstance(Enum.InternalGetUnderlyingType(this), count);
-            else
-                result = Array.CreateInstance(this, count);
-            Array.Copy(values, result, values.Length);
-            return result;
+            // Compat: we should be returning SomeInt32Enum[]. Instead we return Int32[].
+            // This is a tradeoff since SomeInt32Enum[] type might not have been pregenerated.
+            return (Array)Enum.GetEnumInfo(this).ValuesAsUnderlyingType.Clone();
         }
 
         internal bool IsActualEnum

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

@@ -315,7 +315,6 @@ public static TEnum[] GetValues<TEnum>() where TEnum : struct, Enum =>
             (TEnum[])GetValues(typeof(TEnum));
 #endif
 
-        [RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload instead.")]
         public static Array GetValues(Type enumType)
         {
             ArgumentNullException.ThrowIfNull(enumType);

src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs

@@ -99,7 +99,6 @@ public sealed override Type MakeArrayType(int rank)
         public sealed override string GetEnumName(object value) => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override string[] GetEnumNames() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override Type GetEnumUnderlyingType() => throw new NotSupportedException(SR.NotSupported_SignatureType);
-        [RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use Enum.GetValues<TEnum> instead.")]
         public sealed override Array GetEnumValues() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override Guid GUID => throw new NotSupportedException(SR.NotSupported_SignatureType);
         protected sealed override TypeCode GetTypeCodeImpl() => throw new NotSupportedException(SR.NotSupported_SignatureType);

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

@@ -118,7 +118,6 @@ public override string[] GetEnumNames()
             return new ReadOnlySpan<string>(ret).ToArray();
         }
 
-        [RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload instead.")]
         public override Array GetEnumValues()
         {
             if (!IsActualEnum)

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

@@ -515,7 +515,6 @@ public virtual Type GetEnumUnderlyingType()
             return fields[0].FieldType;
         }
 
-        [RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use Enum.GetValues<TEnum> instead.")]
         public virtual Array GetEnumValues()
         {
             if (!IsEnum)

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

@@ -2312,7 +2312,6 @@ protected Enum() { }
         public static string[] GetNames<TEnum>() where TEnum: struct, System.Enum { throw null; }
         public System.TypeCode GetTypeCode() { throw null; }
         public static System.Type GetUnderlyingType(System.Type enumType) { throw null; }
-        [System.Diagnostics.CodeAnalysis.RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload instead.")]
         public static System.Array GetValues(System.Type enumType) { throw null; }
         public static TEnum[] GetValues<TEnum>() where TEnum : struct, System.Enum { throw null; }
         public bool HasFlag(System.Enum flag) { throw null; }
@@ -5860,7 +5859,6 @@ protected Type() { }
         public virtual string? GetEnumName(object value) { throw null; }
         public virtual string[] GetEnumNames() { throw null; }
         public virtual System.Type GetEnumUnderlyingType() { throw null; }
-        [System.Diagnostics.CodeAnalysis.RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use Enum.GetValues<TEnum> instead.")]
         public virtual System.Array GetEnumValues() { throw null; }
         [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public System.Reflection.EventInfo? GetEvent(string name) { throw null; }