Add support for lower bounds in type parameters

[allcre]

This change implements lower bound constraints for generic type parameters in RBS, allowing declarations like [T > SomeType].

The implementation includes:

• Parser and lexer modifications to handle ">" token in type params
• Relevant changes to the Ruby API, like Locator and Validator
• Schema updates to typeParam.json
• Documentation updates

[allcre]

This change ensures the parser correctly validates syntax after type parameter bounds. Previously, expressions like [T < String Integer] would be silently accepted despite being invalid.

[allcre]

This loop is to parse both upper bound (<) and lower bound (>) constraints for type parameters. The loop runs at most twice to allow both bound types in either order: [T < UpperBound > LowerBound] or [T > LowerBound < UpperBound]. It detects and prevents duplicate bounds of the same type and exits early if no bounds are present.

[ParadoxV5]

Side Note: In RBS, the generic type specify covariance and contravariance with in/out keywords:

class Covariant[out O] …
class Contravariant[in I] …

def example(src, dst) #: [T] (Covariant[T], Contravariant[T]) -> void
  dst.set src.get
end

Java generics are invariant; instead, each application specifies co- and contravariance through wildcard lower and upper bounds case-by-case:

class Covariant<O> …
class Contravariant<I> …

<T> void example(Covariant<? extends T> src, Contravariant<? super T> dst) {
  dst.set(src.get());
}

In RBS, that is equivalent to:

class Covariant[O] …
class Contravariant[I] …

def example: [T, O < T = T, I > T = T] (Covariant[O], Contravariant[I]) -> void

[soutaro]

Thank you! 🎉