Make System.Net.Http.HPack.IntegerEncoder a struct (#54209)

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackDecoder.cs

@@ -83,7 +83,7 @@ private enum State : byte
         private readonly int _maxDynamicTableSize;
         private readonly int _maxHeadersLength;
         private readonly DynamicTable _dynamicTable;
-        private readonly IntegerDecoder _integerDecoder = new IntegerDecoder();
+        private IntegerDecoder _integerDecoder;
         private byte[] _stringOctets;
         private byte[] _headerNameOctets;
         private byte[] _headerValueOctets;

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/IntegerDecoder.cs

@@ -6,7 +6,7 @@
 
 namespace System.Net.Http.HPack
 {
-    internal sealed class IntegerDecoder
+    internal struct IntegerDecoder
     {
         private int _i;
         private int _m;

src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackDecoder.cs

@@ -123,7 +123,7 @@ private enum State
         private int _headerValueLength;
         private int _stringLength;
         private int _stringIndex;
-        private readonly IntegerDecoder _integerDecoder = new IntegerDecoder();
+        private IntegerDecoder _integerDecoder;
 
         private static ArrayPool<byte> Pool => ArrayPool<byte>.Shared;