Support unsealed array shape syntax

[bmewburn]

/** @return array{a: mixed, ...<array-key, mixed>} */
function test(): array {
    return ['a' => 1, 'b' => 'b'];
}

https://psalm.dev/articles/psalm-5 https://github.com/phpstan/phpstan/issues/8438 https://github.com/vimeo/psalm/issues/8804