Add `groupBy()` for matching about t-regx HOT 2 CLOSED

pattern('\d+(?<unit>cm|mm)')->match('12cm 14mm 13cm 19cm 18mm 2mm')->groupBy('unit')
  ->map('strlen');

[
  'cm' => [4, 4, 4],
  'mm' => [4, 4, 3]
]

pattern('\d+(?<unit>cm|mm)')->match('12cm 14mm 13cm 19cm 18mm 2mm')->groupBy('unit')
  ->flatMap('str_split');

[
  'cm' => ['1', '2', 'c', 'm', '1', '3', 'c', 'm', '1', '9', 'c', 'm'],
  'mm' => ['1', '4', 'm', 'm', '1', '8', 'm', 'm', '2', 'm', 'm']
]