The *_from_string() and resolve_*_alias() generated methods are the last
remaining users of HashMap in the LibUnicode generated files (read: the
last methods not using compile-time structures). This converts these
methods to use an array containing pairs of hash values to the desired
lookup value.
Because this code generation is the same between GenerateUnicodeData.cpp
and GenerateUnicodeLocale.cpp, this adds a GeneratorUtil.h header to the
LibUnicode generators to contain the method that generates the methods.
