Fix EZP-20608 eZRest v2 : Not possible to set fieldSetting "textRows" for contentfieldtype "eztext"

This PR fixes issue https://jira.ez.no/browse/EZP-20608

Validator configuration and field settings are now parsed from FieldDefinitionCreateStruct.
Conversion of constants, booleans and integers from field settings and validator configuration hashes is done in FieldType class implementation.

## TODO
- [ ] parse settings and validators in FieldDefinitionUpdateStruct