Added mk_translucent_accessor() and mk_class_accessor()

The former is simply an alias for mk_translucent() (the old name is kept
for backwards compatibility); the latter is an improved version of
mk_classdata() from Class::Data::Inheritable which resolves that module's
long-outstanding CPAN RT#51228 and CPAN RT#6281 since its maintainer seems
 unwilling to resolve them in Class::Data::Inheritable.

Also imported Class::Data::Inheritable's t/Inheritable.t test script as
t/03-class_tests.t to test that mk_class_accessor() is working correctly.