ECIEncoderSet
Set of CharsetEncoders for a given input string
Invariants:
The list contains only encoders from CharacterSetECI (list is shorter then the list of encoders available on the platform for which ECI values are defined).
The list contains encoders at least one encoder for every character in the input.
The first encoder in the list is always the ISO-8859-1 encoder even of no character in the input can be encoded by it.
If the input contains a character that is not in ISO-8859-1 then the last two entries in the list will be the UTF-8 encoder and the UTF-16BE encoder.