[Validator] Support "maxSize" given in KiB

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | symfony/symfony#10962


To display the constraint validation message with an expected suffix, this PR add a new option in  File constraint.
For ``1000`` I could agree. But when talking about 1,000,000 or higher, having a separator increases readability. Thus, I would stick with the way it is done in written English.