Add missing ArrayAccess Stubs for Ds extension Class

[josephLaurent]

The issue is describe here : #11512

https://psalm.dev/r/ae327d30c9

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/ae327d30c9

<?php
use Ds\Map;

/** @var Map<string, int> */
$mapObj = new Map(['a' => 17]);

$integer = $mapObj['a']; // ERROR

$otherInteger = $mapObj->get('a'); // WORK FINE

$mapObj['b'] ??= 35; // ERROR

Psalm output (using commit cdceda0):

INFO: MixedAssignment - 7:1 - Unable to determine the type that $integer is being assigned to

INFO: MixedAssignment - 11:1 - Unable to determine the type of this assignment