…(ivannemets-sravniru)

This PR was squashed before being merged into the 5.4 branch.

Discussion
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[Serializer] #36594 attributes cache breaks normalization

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #36594
| License       | MIT
| Doc PR        | symfony/symfony-docs#15823

The bug itself is explained in the following (simplified) example:
```php
class Dummy
{
    public array $requiredData; // supposed to be set for any object
    public array $optionalData; // can be not initialized (and if so - ignored by serializer)
}

$object1 = new Dummy();
$object1->requiredData = ['username' => 'foo'];
$json1 = $serializer->serialize($object1, 'json'); // {"requiredData": {"username": "foo"}}
// at this point object normalizer has already cached attributes for Dummy::class and context,
// now it contains array ['requiredData'] - optionalData has been ignored as it's unitialized

// then, while the script is still running, we have another object of the same class with optionalData set
$object2 = new Dummy();
$object2->requiredData = ['username' => 'bar'];
$object2->optionalData = ['email' => 'bar@test.com'];
$json2 = $serializer->serialize($object2, 'json');
// expected: {"requiredData": {"username": "bar"}, "optionalData": {"email": "bar@test.com"}}
// actual: {"requiredData": {"username": "bar"}}
// here normalizer has no clue about optionalData attribute since it reuses attributes cached
// in \Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer::$attributesCache
// while normalizing the first object
```

Though this PR created for 5.4 branch, it actually fixes a bug reproducible in 5.3. The reason why I use 5.4 for this fix is that 5.4 introduces a [new feature](symfony/symfony-docs#15823) related to the same problem. If this PR gets approved and merged, I can potentially implement the same fix for 5.3, but `SKIP_UNINITIALIZED_VALUES` will cause some merge conflicts in the future..

As of v 5.3 symfony ignores uninitialized properties by default in `ObjectNormalizer::extractAttributes` and `PropertyNormalizer::extractAttributes` (implemented in #38900 and #34791) but this approach is wrong - **`extractAttributes` method MUST return the same attributes list for any instance of the same class**, otherwise cached attributes do not match actual attributes list for different instances having different set of initialized/uninitialized properties

So, this PR does a few things:

1. removes ignoring attributes from all built-in implementations of `\Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer::extractAttributes` so that even uninitialized attributes will be cached by normalizer. Instead, we ignore uninitialized attributes when trying to access them while calling `\Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer::getAttributeValue`
2. sets `true` as the default value for `SKIP_UNINITIALIZED_VALUES` context setting as I believe this is the expected default behavior for any built-in object normalizer
3. makes `SKIP_UNINITIALIZED_VALUES` compatible with not just `ObjectNormalizer`, but with two other built-in normalizers `PropertyNormalizer` and `GetSetMethodNormalizer` as well

Commits
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55818c3 [Serializer] #36594 attributes cache breaks normalization