Avoid int[] allocation in ResourceReader when reading a decimal (dotnet#60408)

Author: stephentoub

src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.cs

@@ -575,7 +575,11 @@ private unsafe string AllocateStringForNameIndex(int index, out int dataOffset)
                 return new TimeSpan(_store.ReadInt64());
             else if (type == typeof(decimal))
             {
+#if RESOURCES_EXTENSIONS
                 int[] bits = new int[4];
+#else
+                Span<int> bits = stackalloc int[4];
+#endif
                 for (int i = 0; i < bits.Length; i++)
                     bits[i] = _store.ReadInt32();
                 return new decimal(bits);