[EAK-527] Enhance StringTransformation routine

[smiakchilo]

As an EAK user, I aplly @OptionSource with enums or constant classes used as the source of data for dropdown lists. An enum constant is usually spelled in the format like DARK_GRAY. To convert it into an option label, I would use textTransform = StringTransformation.CAPITALIZE. However this transformation does not process underscore separator although it does process dashes.

I would like to have DARK_GRAY converted to "Dark Gray" when StringTransformation.CAPITALIZE` is used.

Also, they need to make sure that the same word-separatio/conversion principles are used with all the available transformers.