[Form] Removed usage of the ChoiceList::getIndicesFor*() methods where they don't offer any performance benefit
[Form] Fixed ChoiceList::get*By*() methods to preserve order and array keys
[Form] Fixed expanded choice field to be marked invalid when unknown choices are submitted
[Form] Improved test coverage of ChoiceList classes
[DoctrineBridge] Improved test coverage of EntityChoiceList
[Form] Deprecated ChoiceList::getIndicesFor*() methods