[Validator] Support "maxSize" given in KiB
feature #11027 [Validator] Support "maxSize" given in KiB (Jérémy Derussé)

This PR was squashed before being merged into the 2.6-dev branch (closes #11027).

Discussion
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[Validator] Support "maxSize" given in KiB

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10962
| License       | MIT
| Doc PR        | symfony/symfony-docs#3895

To display the constraint validation message with an expected suffix, this PR add a new option in  File constraint.

Commits
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48ed754 [Validator] Support "maxSize" given in KiB