YANG parser should bind leaf-instantiated leafref paths

Since YANGTOOLS-969 introduced support for parsing leafref path expressions, this support is not complete, as it does not perform binding of unqualified QNames when a leaf is completely instantiated.

As a first step, we should recognize when we are parsing the argument value in an instantiated-leaf case and perform full binding.

As the second step, we should hook onto StatementSupport.adaptArgumentValue() and intercept the case when leaves from groupings are landing in their final instantiation. This may require some trickery, as type statements are reused when they are copied.

The third step, which is probably related to the second one, is how to validate typedef references when they are used in leaves.

Finally we need to define how binding relates to LeafrefTypeDefinition, as currently we do not have an avenue how to update an the path expression and our users are doing dirty tricks to parse them out.