[Validator] Fix constraint violation message parameterization
[Validator] Fixed value-to-string conversion in constraint violations
[Validator] Simplified IBAN validation algorithm
[Validator] Fixed and simplified IsbnValidator
[Validator] Simplified IssnValidator
[Validator] Simplified and explained the LuhnValidator
[Validator] Added "{{ value }}" parameters where they were missing
[Validator] Fixed date-to-string conversion tests to match ICU 51
[Validator] Fixed CS
[Validator] Renamed valueToString() to formatValue(); added missing formatValue() calls
[Validator] Removed information from the violation output if the value is an array, object or resource

This was decided in the discussion of #10687.
[Validator] Added more detailed inline documentation