[ja] Add "CLI.generator.className.test", "Validation.field_exists"

[kenjis]

Description Update for v4.5.0.

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [x] Conforms to style guide

[kenjis]

Okay, GA checks passed.