The class `\CuyZ\Valinor\Mapper\Tree\Node` has been refactored to remove
access to unwanted methods that were not supposed to be part of the
public API. Below are a list of all changes:
- New methods `$node->sourceFilled()` and `$node->sourceValue()` allow
accessing the source value.
- The method `$node->value()` has been renamed to `$node->mappedValue()`
and will throw an exception if the node is not value.
- The method `$node->type()` now returns a string.
- The methods `$message->name()`, `$message->path()`, `$message->type()`
and `$message->value()` have been deprecated in favor of the new
method `$message->node()`.
- The message parameter `{original_value}` has been deprecated in favor
of `{source_value}`.
