[Form] Changed (Number|Integer)ToLocalizedStringTransformer::reverseTransform() to do rounding

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #8473
| License       | MIT
| Doc PR        | symfony/symfony-docs#2872