[Validator] Deprecate use of `Locale` validation constraint without setting "canonicalize" option to `true`

[javiereguiluz]

We recently documented this feature, so we just need to add that not using it is deprecated. See symfony/symfony#26075.

[snoek09]

Wasn't this fixed in https://github.com/symfony/symfony-docs/pull/9248/files#diff-08df604c59d5284048fac6277839ca0dR104?

[xabbuh]

fixed by #9248