Fix shifting a negative value when using BigInts (#4429)

When shifting a negative BigInt value if the
shift count is very "big" the result should be -1.

eg.:
```
(-2n >> (2n*32n)) === -1n
```

Note: the `-2n >> (2n*31n)` already returned `-1n` prior this change.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com

jerry-core/ecma/operations/ecma-bigint.c

@@ -1412,6 +1412,11 @@ ecma_bigint_shift (ecma_value_t left_value, /**< left BigInt value */
     {
       return ecma_bigint_raise_memory_error ();
     }
+    else if (left_p->u.bigint_sign_and_size & ECMA_BIGINT_SIGN)
+    {
+      /* Shifting a negative value with a very big number to the right should be -1. */
+      return ecma_bigint_create_from_digit (1, true);
+    }
 
     return ECMA_BIGINT_ZERO;
   }