[Form] Fixed issue in BaseDateTimeTransformer when invalid timezone cause Trans...

...formation filed exception (closes #9403).

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9403
| License       | MIT
| Doc PR        | 

DateTimeZone object creation could rise an exception. So in BaseDateTimeTransformer constructor we need to check if timezone is valid. If this exception is catched and rethrowed as TransformationFailed exception we have an issue: user will see "Invalid value" error in form, but issue is actually with php configuration or form type configuration.

Replaces #9772.