minor symfony#61871 [Validator] Improve and complete Japanese translations (GK-302)

This PR was squashed before being merged into the 6.4 branch. Discussion ---------- [Validator] Improve and complete Japanese translations | Q | A | ------------- | --- | Branch? | 6.4 | Bug fix? | yes | New feature? | no | Deprecations? | no | Issues | Fix symfony#61634 | License | MIT Hello! This PR adds the missing Japanese translations for the validator component and refactors the entire file for consistency. I have updated the `validators.ja.xlf` file by adding all missing translations. Additionally, I performed a full review of the **entire file, including existing human-translated messages,** and refactored them based on a unified style guide. This was done to improve the overall quality and fix inconsistencies in style, tone, and formatting (e.g., standardizing on expressions like `〜ではありません`, `〜でなければなりません`, etc.). I'm happy to discuss any of these changes or make further adjustments. Please let me know what you think. Thank you! Commits ------- 4a40f3c [Validator] Improve and complete Japanese translations

Author: fabpot