[11.x] Rework Context::stackContains with Closures.

[timacdonald]

This PR re-works how Context::stackContains works with closures to make it line up with how Collection::contains works.

Before, the closure passed to Context::stackContains would receive the entire stack. I believe it should be passed each individual item and have a truth test performed on the item.

Context::push('stack-name', 'value-1');
Context::push('stack-name', 'value-2');
Context::push('stack-name', 'value-3');

Context::stackContains('stack-name', function (string $value) {
    // $value will be "value-1" then "value-2" then "value-3"

    return str_ends_with($value, '-2');
});

Previously, the closure received the entire stack.

Context::stackContains('stack-name', function (array $stack) {
    // $value is ["value-1",  "value-2", "value-3"]
});

[timacdonald]

This is a bugfix as well because it was not checking the hidden data.

[devajmeireles]

I was already going to notify you about this after I read the other PR 😂