Get paths for documentable definitions
These are used to:
If T is nullable, it should return null if the definition does not exist.
namespace Facebook\HHAPIDoc;
interface IPathProvider {...}
->getPathForClass(string $class): T->getPathForClassMethod(string $class, string $method): T->getPathForFunction(string $function): T->getPathForInterface(string $interface): T->getPathForInterfaceMethod(string $interface, string $method): T->getPathForOpaqueTypeAlias(string $name): T->getPathForTrait(string $trait): T->getPathForTraitMethod(string $trait, string $method): T->getPathForTransparentTypeAlias(string $name): T