restored SqlTypeWorkarounds.SqlGuidCtor for non .NET8 tagrets

This reverts commit 288a70c partially

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlTypes/SqlTypeWorkarounds.netcore.cs

@@ -122,5 +122,31 @@ private struct SqlBinaryCaster
             internal SqlBinaryLookalike Fake;
         }
         #endregion
+
+        #region Work around inability to access SqlGuid.ctor(byte[], bool)
+        internal static SqlGuid SqlGuidCtor(byte[] value, bool ignored)
+        {
+            // Construct a SqlGuid without allocating/copying the byte[].  This provides
+            // the same behavior as SqlGuid.ctor(byte[], bool).
+            var c = default(SqlGuidCaster);
+            c.Fake._value = value;
+            return c.Real;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct SqlGuidLookalike
+        {
+            internal byte[] _value;
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        private struct SqlGuidCaster
+        {
+            [FieldOffset(0)]
+            internal SqlGuid Real;
+            [FieldOffset(0)]
+            internal SqlGuidLookalike Fake;
+        }
+        #endregion
     }
 }