Implement BigInt.prototype[ @@toStringTag ]

[n14little]

This Pull Request fixes/closes #1230.

It changes the following:

• Implements BigInt.prototype[ @@toStringTag ]

[n14little]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,701	78,701	0
Passed	26,400	26,404	+4
Ignored	15,519	15,519	0
Failed	36,782	36,778	-4
Panics	26	26	0
Conformance	33.54%	33.55%	+0.01%

[n14little]

Benchmarks:

┌─────────┬──────────────────────────────────────────────┬──────────────────────┬──────────────────────┬────────────┐
│ (index) │                     name                     │   changesDuration    │    masterDuration    │ difference │
├─────────┼──────────────────────────────────────────────┼──────────────────────┼──────────────────────┼────────────┤
│    0    │     'Arithmetic operations (Execution)'      │ '**358.2±12.21ns**'  │   '360.5±14.49ns'    │  '-0.99'   │
│    1    │        'Arithmetic operations (Full)'        │ '**288.3±10.97µs**'  │   '294.3±27.24µs'    │   '-2.0'   │
│    2    │          'Array access (Execution)'          │     '6.6±0.22µs'     │   '**6.5±0.40µs**'   │   '+2.0'   │
│    3    │            'Array access (Full)'             │   '326.9±26.75µs'    │ '**321.9±26.22µs**'  │   '+2.0'   │
│    4    │         'Array creation (Execution)'         │   '**2.7±0.11ms**'   │     '2.8±0.21ms'     │   '-2.9'   │
│    5    │           'Array creation (Full)'            │   '**3.2±0.16ms**'   │     '3.3±0.41ms'     │  '-0.99'   │
│    6    │           'Array pop (Execution)'            │ '**853.8±32.12µs**'  │   '873.4±40.91µs'    │   '-2.0'   │
│    7    │              'Array pop (Full)'              │ '**1431.9±82.78µs**' │   '1453.5±75.04µs'   │   '-2.0'   │
│    8    │     'Boolean Object Access (Execution)'      │     '5.3±0.24µs'     │     '5.4±0.40µs'     │   '0.0'    │
│    9    │        'Boolean Object Access (Full)'        │   '312.1±10.74µs'    │   '312.0±23.63µs'    │   '0.0'    │
│   10    │            'Clean js (Execution)'            │   '680.1±27.99µs'    │   '680.7±16.34µs'    │   '0.0'    │
│   11    │              'Clean js (Full)'               │ '**1016.2±65.80µs**' │  '1034.2±119.14µs'   │   '-2.0'   │
│   12    │             'Clean js (Parser)'              │  '**43.6±1.57µs**'   │    '43.9±1.72µs'     │  '-0.99'   │
│   13    │                'Create Realm'                │   '421.7±29.24ns'    │ '**410.4±23.44ns**'  │   '+3.0'   │
│   14    │ 'Dynamic Object Property Access (Execution)' │   '**5.4±0.20µs**'   │     '5.4±0.27µs'     │  '-0.99'   │
│   15    │   'Dynamic Object Property Access (Full)'    │   '315.6±16.33µs'    │   '316.4±24.88µs'    │   '0.0'    │
│   16    │            'Expression (Parser)'             │     '7.0±0.31µs'     │   '**6.9±0.41µs**'   │   '+1.0'   │
│   17    │           'Fibonacci (Execution)'            │   '846.6±32.94µs'    │ '**826.9±37.92µs**'  │   '+2.0'   │
│   18    │              'Fibonacci (Full)'              │   '1191.1±66.17µs'   │ '**1184.9±70.60µs**' │   '+1.0'   │
│   19    │            'For loop (Execution)'            │    '23.1±0.90µs'     │  '**22.5±1.06µs**'   │   '+3.0'   │
│   20    │              'For loop (Full)'               │ '**328.5±12.31µs**'  │   '345.1±91.18µs'    │   '-4.8'   │
│   21    │             'For loop (Parser)'              │  '**20.7±0.86µs**'   │    '20.9±1.34µs'     │  '-0.99'   │
│   22    │           'Goal Symbols (Parser)'            │    '14.2±0.45µs'     │  '**14.1±0.39µs**'   │   '+1.0'   │
│   23    │            'Hello World (Parser)'            │     '4.0±0.36µs'     │     '4.0±0.14µs'     │   '0.0'    │
│   24    │             'Long file (Parser)'             │ '**789.2±21.90ns**'  │   '811.8±83.81ns'    │   '-2.9'   │
│   25    │            'Mini js (Execution)'             │ '**603.8±18.06µs**'  │   '609.7±18.77µs'    │  '-0.99'   │
│   26    │               'Mini js (Full)'               │ '**934.5±35.21µs**'  │   '943.3±24.50µs'    │  '-0.99'   │
│   27    │              'Mini js (Parser)'              │    '38.1±2.22µs'     │  '**37.5±1.03µs**'   │   '+2.0'   │
│   28    │      'Number Object Access (Execution)'      │     '4.2±0.14µs'     │   '**4.2±0.16µs**'   │   '+1.0'   │
│   29    │        'Number Object Access (Full)'         │   '306.5±12.64µs'    │  '**304.5±9.19µs**'  │   '+1.0'   │
│   30    │        'Object Creation (Execution)'         │     '4.7±0.30µs'     │     '4.7±0.31µs'     │   '0.0'    │
│   31    │           'Object Creation (Full)'           │  '**308.9±8.32µs**'  │    '314.4±9.69µs'    │   '-2.0'   │
│   32    │             'RegExp (Execution)'             │    '11.6±0.41µs'     │  '**11.4±0.80µs**'   │   '+2.0'   │
│   33    │               'RegExp (Full)'                │   '331.6±20.58µs'    │ '**324.4±12.54µs**'  │   '+2.0'   │
│   34    │         'RegExp Literal (Execution)'         │    '11.6±0.58µs'     │  '**11.2±0.42µs**'   │   '+3.0'   │
│   35    │           'RegExp Literal (Full)'            │ '**324.5±14.90µs**'  │   '327.4±18.14µs'    │  '-0.99'   │
│   36    │    'RegExp Literal Creation (Execution)'     │  '**10.0±0.43µs**'   │    '10.2±0.68µs'     │   '-2.9'   │
│   37    │       'RegExp Literal Creation (Full)'       │  '**311.4±7.48µs**'  │   '314.0±10.33µs'    │  '-0.99'   │
│   38    │ 'Static Object Property Access (Execution)'  │   '**4.9±0.18µs**'   │     '5.0±0.26µs'     │   '-2.0'   │
│   39    │    'Static Object Property Access (Full)'    │ '**316.9±12.77µs**'  │   '319.6±22.93µs'    │  '-0.99'   │
│   40    │      'String Object Access (Execution)'      │   '**7.6±0.24µs**'   │     '7.8±0.27µs'     │   '-2.0'   │
│   41    │        'String Object Access (Full)'         │ '**315.0±23.23µs**'  │   '322.4±27.23µs'    │   '-2.0'   │
│   42    │       'String comparison (Execution)'        │     '6.8±0.31µs'     │     '6.8±0.27µs'     │   '0.0'    │
│   43    │          'String comparison (Full)'          │   '316.5±14.27µs'    │   '315.9±11.89µs'    │   '0.0'    │
│   44    │      'String concatenation (Execution)'      │   '**5.5±0.26µs**'   │     '5.6±0.30µs'     │   '-2.0'   │
│   45    │        'String concatenation (Full)'         │   '313.2±21.66µs'    │ '**308.7±10.43µs**'  │   '+1.0'   │
│   46    │          'String copy (Execution)'           │   '**4.2±0.39µs**'   │     '4.3±0.17µs'     │   '-2.0'   │
│   47    │             'String copy (Full)'             │   '303.7±11.36µs'    │  '**301.4±9.94µs**'  │   '+1.0'   │
│   48    │            'Symbols (Execution)'             │   '**3.6±0.22µs**'   │     '3.6±0.36µs'     │   '-2.9'   │
│   49    │               'Symbols (Full)'               │  '**290.1±7.37µs**'  │   '294.3±31.94µs'    │  '-0.99'   │
│   50    │                      ''                      │      undefined       │      undefined       │   '+NaN'   │
└─────────┴──────────────────────────────────────────────┴──────────────────────┴──────────────────────┴────────────┘