Improve bytes conversion method

This PR improves bytes conversion `regex` method introduced in #7413 (thanks to @vicb's comments).

* Adds support of `+` prefix.
* Adds support of blank chars between `+`, number and unit.
* Adds support of octal/hexa bases.

Notice that this can not be unit tested for `ServerParams` and `UploadedFile` classes because `ini_set()` function does not work with `post_max_size` and `upload_max_filesize` settings.

For information, this convertion is located in 3 classes:
* `Symfony\Component\Form\Extension\Validator\Util\ServerParams`
* `Symfony\Component\HttpFoundation\File\UploadedFile`
* `Symfony\Component\HttpKernel\DataCollector\MemoryDataCollector`

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7413