Improve BigInt support (#4118)

This patch adds several small features:
- Support right shift with negative numbers
- Support exponentation operator
- BigInts can be enabled in ES5.1 mode
- Remove dead code from ecma_deref_bigint
- Support longer BigInt literals in the parser
- Fix various BigInt comparison issues
- Do not discard unary plus for BigInt constants

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/ecma/operations/ecma-big-uint.h

@@ -59,6 +59,11 @@ typedef uint64_t ecma_bigint_two_digits_t;
 #define ECMA_BIGINT_HIGH_DIGIT(digit) \
   (((ecma_bigint_two_digits_t) digit) << (8 * sizeof (ecma_bigint_digit_t)))
 
+/**
+ * Tells whether a number (usually a digit or uint32_t value) is an odd number.
+ */
+#define ECMA_BIGINT_NUMBER_IS_ODD(number) ((number & 0x1) != 0)
+
 /**
  * Bitwise operation types.
  */
@@ -117,7 +122,12 @@ ecma_extended_primitive_t *ecma_big_uint_div_mod (ecma_extended_primitive_t *div
                                                   bool is_mod);
 
 ecma_extended_primitive_t *ecma_big_uint_shift_left (ecma_extended_primitive_t *left_value_p, uint32_t right_value);
-ecma_extended_primitive_t *ecma_big_uint_shift_right (ecma_extended_primitive_t *left_value_p, uint32_t right_value);
+ecma_extended_primitive_t *ecma_big_uint_shift_right (ecma_extended_primitive_t *left_value_p, uint32_t right_value,
+                                                      bool increase_result);
+
+#if ENABLED (JERRY_ESNEXT)
+ecma_extended_primitive_t *ecma_big_uint_pow (ecma_extended_primitive_t *left_value_p, uint32_t right_value);
+#endif /* ENABLED (JERRY_ESNEXT) */
 
 ecma_extended_primitive_t *ecma_big_uint_bitwise_op (uint32_t operation_and_options,
                                                      ecma_extended_primitive_t *left_value_p,