This encapsulates the logic for turning an acceptable preset name into
the absolute path for that preset. It can be used to preprocess a
presets list to map each preset to its absolute path, which is necessary
if `babel.transform` is going to be executed on a file outside the
directory subtree where the presets are installed.
This adds a getPossiblePresetNames helper encapsulating the logic for
what preset names we should try to resolve, and the resolvePreset method
just calls this helper and actually resolves them.
