[DI] Resolve iterator argument as plain array if required

[ro0NL]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes/no
Fixed tickets	#...
License	MIT
Doc PR	symfony/symfony-docs#...

Given

class Foo {
    private $bars;
    public function __construct(array $bars) {
        $this->bars = $bars;
    }
}

services:
    a: { class: stdClass }
    b: { class: stdClass }
    Foo: [!iterator ['@a', '@b']]

dump($this->get(Foo::class));

Before

Catchable Fatal Error: Argument 1 passed to AppBundle\Foo::__construct() must be of the type array, object given

After

Foo {#223 ▼
  -bars: array:2 [▼
    0 => {#224}
    1 => {#222}
  ]
}

[nicolas-grekas]

👎 the config should be fixed instead.

[ro0NL]

on 2nd thought this should probably just be built-in with #22200