Allows defining a new type that is the combination of an existing type and custom constraints

A subtle difference between this type and its supertype (one that will almost certainly not matter in any case) is that we use the apply_constraints logic of the underlying type in the same step as cast_input. We do this because new types like these are, generally speaking, considering the constraint application as part of the core type. Other types, if you simply do Ash.Type.cast_input/3 you will not be also applying their constraints.

For Example:

defmodule MyApp.Types.SSN do
  use Ash.Type.NewType, subtype_of: :string, constraints: [match: ~r/regex for ssn/]
end

defmodule MyApp.Types.Metadata do
  use Ash.Type.NewType, subtype_of: :union, constraints: [types: [
    foo: [...],
    bar: [...]
  ]]
end