[12.x] Add fromJson() to Arr helper

[shaedrich]

Counterpart of #56697, so to speak

Examples

Arr::fromJson('}', false, 512, 0); // ❌ Throws 'Please provide a valid JSON: Syntax error'
Arr::fromJson("[\"\u{D800}\"]", false, 512, 0); // ❌ Throws 'Please provide a valid JSON: Malformed UTF-8 characters, possibly incorrectly encoded'
Arr::fromJson('[[[[]]]]', false, 2, 0); // ❌ Throws 'Please provide a valid JSON: Maximum stack depth exceeded'
Arr::fromJson('null', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: null given instead'
Arr::fromJson('42', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: int given instead'
Arr::fromJson('42.1', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: float given instead'
Arr::fromJson('"foo"', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: string given instead'
Arr::fromJson('true', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: bool given instead'
Arr::fromJson('{"foo": "bar"}', false, 512, 0); // ❌ Throws 'The given JSON cannot be parsed into an array: stdClass given instead'

Arr::fromJson('[1, 2, 3]', false, 512, 0); // ✔️ [1, 2, 3]
Arr::fromJson('[1, 2, 3]', null, 512, JSON_OBJECT_AS_ARRAY); // ✔️ [1, 2, 3]
Arr::fromJson('[1, 2, 3]', true, 512, 0); // ✔️ [1, 2, 3]
Arr::fromJson('{"foo": "bar"}', null, 512, JSON_OBJECT_AS_ARRAY); // ✔️ ["foo" => "bar"]
Arr::fromJson('{"foo": "bar"}', true, 512, 0); // ✔️ ["foo" => "bar"]