Cleanup: Move _yaml.node_get_project_path() to Project._get_path_from_node()

Description

node_get_project_path() is currently only being called within Project and by Plugin._get_path_from_node().

This patch lifts node_get_project_path() out of _yaml.py to a private member function of Project, where it has been renamed to _get_path_from_node().

Considering there is no YAML related behavior in this function, it makes sense to move it from this module.