Make DiacriticsMapping protected

[Poltuu]

In this PR, I suggest to make DiacriticsMapping protected.

I had define my own DiacriticsMapper, but I wanted to use the DefaultDiacriticsMapper as a base class, since it basically was exactly what I needed and I could not find a "simple" entry point without redefining too much in my opinion, hende this PR.

Also, I could not help myself and modified the UpdateMappings method to save a loop on mappings and an allocation of the all List, as well as the HasDiacritics to stop at first encounter of a diacritics