Fix NETCORE to NET8(or newer) directive

ICSharpCode.Decompiler/Util/BitOperations.cs

@@ -2,7 +2,7 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
-#if !NETCORE
+#if !NET8_0_OR_GREATER
 namespace System.Numerics
 {
 	internal static class BitOperations

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -14,7 +14,7 @@ namespace ICSharpCode.Decompiler.Util
 			value = pair.Value;
 		}
 
-#if !NETCORE
+#if !NET8_0_OR_GREATER
 		public static IEnumerable<(A, B)> Zip<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
 		{
 			return input1.Zip(input2, (a, b) => (a, b));
@@ -66,7 +66,7 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-#if !NETCORE
+#if !NET8_0_OR_GREATER
 		public static HashSet<T> ToHashSet<T>(this IEnumerable<T> input)
 		{
 			return new HashSet<T>(input);
@@ -312,6 +312,8 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
+
+#if !NET8_0_OR_GREATER
 		/// <summary>
 		/// Returns the maximum element.
 		/// </summary>
@@ -320,7 +322,7 @@ namespace ICSharpCode.Decompiler.Util
 		{
 			return source.MaxBy(keySelector, Comparer<K>.Default);
 		}
-
+#endif
 		/// <summary>
 		/// Returns the maximum element.
 		/// </summary>
@@ -377,7 +379,7 @@ namespace ICSharpCode.Decompiler.Util
 			return first;
 		}
 
-#if !NETCORE
+#if !NET8_0_OR_GREATER
 		public static int EnsureCapacity<T>(this List<T> list, int capacity)
 		{
 			if (capacity < 0)

ICSharpCode.Decompiler/Util/KeyComparer.cs

@@ -81,7 +81,8 @@ namespace ICSharpCode.Decompiler.Util
 
 		public int GetHashCode(TElement obj)
 		{
-			return keyEqualityComparer.GetHashCode(keySelector(obj));
+			var key = keySelector(obj)!;
+			return keyEqualityComparer.GetHashCode(key);
 		}
 	}
 }