LPS-51839 add validation tests
LPS-51839 add validation entities

Create a new `ContentReference` class to represent the contents of a
FileEntry and a generic interface `ModelValidator`.

This will allow users to write and/or override default file entry
content validations.
LPS-51839 create validation util class

This class will allow consumers of the API to access default Liferay
validators (only file size for the moment), and general validator
operations (right now, only validator composition).
LPS-51839 remove hardcoded validations

Remove hardcoded validation from wrapper, passing the validation object
itself. This way, each repository definer can specify its own
validations.
LPS-51839 extract new size validation method
LPS-51839 reuse validation logic
LPS-51839 rename validation wrappers
LPS-51839 extract variables to make code clearer
LPS-51839 SF