Fix: boolean[] - eatArray() with boolean typed arrays and user defaults

[juergba]

Description

var args = parse('--file --file', {
    array: ['file'],
    boolean: ['file'],
    configuration: {
      'duplicate-arguments-array': true,
      'flatten-duplicate-arrays': false
    }
})      // { _: [], file: [ [], [], [] ] }

The result is incorrect, it should be: { _: [], file: [ [true], [true] ] }

Description of Change

• eatArray() is called even for flags without arguments. This enables to set:
  • boolean with short syntax ('--bool --bool') which carries its implicit value true
  • default values given by opts.default for all type of options (except boolean)
• the fallback default value for all type of options is an empty array [].
• eatArray(): remove the multipleArrayFlag logic. The "duplicate array" pattern is already handled within setKey() depending on the flatten-duplicate-arrays configuration option. setKey() remains unchanged.

[bcoe]

@juergba this is looking like a reasonable start to me, looks like there's an outstanding TODO?

[bcoe]

@juergba 👋 just following up, would love to see this over the finish line.

[bcoe]

@juergba thank you, this looks great.