Sync shared code from runtime (#42276)

Co-authored-by: Tratcher <Tratcher@users.noreply.github.com>

src/Shared/runtime/Http2/Hpack/IntegerDecoder.cs

@@ -73,7 +73,7 @@ namespace System.Net.Http.HPack
                 throw new HPackDecodingException(SR.net_http_hpack_bad_integer);
             }
 
-            _i = _i + ((b & 0x7f) << _m);
+            _i += ((b & 0x7f) << _m);
 
             // If the addition overflowed, the result will be negative.
             if (_i < 0)
@@ -81,7 +81,7 @@ namespace System.Net.Http.HPack
                 throw new HPackDecodingException(SR.net_http_hpack_bad_integer);
             }
 
-            _m = _m + 7;
+            _m += 7;
 
             if ((b & 128) == 0)
             {

src/Shared/runtime/Http2/Hpack/IntegerEncoder.cs

@@ -50,7 +50,7 @@ namespace System.Net.Http.HPack
                     return false;
                 }
 
-                value = value - ((1 << numBits) - 1);
+                value -= ((1 << numBits) - 1);
                 int i = 1;
 
                 while (value >= 128)
@@ -63,7 +63,7 @@ namespace System.Net.Http.HPack
                         return false;
                     }
 
-                    value = value / 128;
+                    value /= 128;
                 }
                 destination[i++] = (byte)value;