Deprecated : remove string input / false output from DateFormatTransformer

[shavounet]

Description

Remove deprecated behavior in DateFormatTransformer

Requirements

• Documentation updates
  • Reference
  • Changelog
• Unit tests

Breaking changes

• minor: date_format transformer will not accept string input anymore
• minor: date_format transformer will throw errors on failed output instead of returning false

[xaviermarchegay]

Done in the v4 branch.

Exception if a DateTimeInterface is not passed to the transformer: https://github.com/cleverage/process-bundle/blob/v4-dev/src/Transformer/DateFormatTransformer.php#L35

Unit tests : https://github.com/cleverage/process-bundle/blob/v4-dev/tests/Transformer/DateParserTransformerTest.php#L40