Utility class that captures invariant Java assignability rules (used with generics).
This class operates on all the possible Type subtypes: Class, ParameterizedType, TypeVariable, WildcardType, GenericArrayType.
To make this class easier to understand and maintain, there is a separate isAssignableFrom method for each combination
of possible types. Each of these methods compares two type instances and determines whether the first one is assignable from
the other.
Since Java wildcards are by definition covariant, this class does not operate on wildcards and instead delegates to
CovariantTypes.
TypeVariables are considered a specific unknown type restricted by the upper bound. No inference of type variables is performed.