[Form] Changed Form::getErrors() to return an iterator and added two optional parameters $deep and $flatten
[Form] Changed the default value of $flatten in Form::getErrors() to true
feature #9918 [Form] Changed Form::getErrors() to return an iterator and added two optional parameters $deep and $flatten (webmozart)

This PR was merged into the 2.5-dev branch.

Discussion
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[Form] Changed Form::getErrors() to return an iterator and added two optional parameters $deep and $flatten

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #7205
| License       | MIT
| Doc PR        | -

See the changes in the UPGRADE files for more information.

Commits
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6b3fbb5 [Form] Changed the default value of $flatten in Form::getErrors() to true
a9268c4 [Form] Changed Form::getErrors() to return an iterator and added two optional parameters $deep and $flatten