Updated information about handling validation of embedded forms to Valid constraint
feature #4348 Updated information about handling validation of embedded forms to Valid... (peterrehm)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4348).

Discussion
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Updated information about handling validation of embedded forms to Valid...

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4346

Applied Valid constraint instead of the cascade_validation option since this option is supposed to be deprecated with symfony/symfony#12237

Commits
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b699731 Updated information about handling validation of embedded forms to Valid constraint