Inspector plugin documentation outdated

[alazifk]

Your Godot version: 4.0 Alpha 13 Issue description: can_handle_object and parse_property are now private. _parse_property signature has changed.

URL to the documentation page: https://docs.godotengine.org/en/latest/tutorials/plugins/editor/inspector_plugins.html?highlight=inspector%20plugin

[If you know how to fix the issue you are reporting please consider opening a pull request. We provide a tutorial on using git here: https://docs.godotengine.org/en/stable/community/contributing/pr_workflow.html, writing documentation at https://docs.godotengine.org/en/stable/community/contributing/docs_writing_guidelines.html and contributing to the class reference here: https://docs.godotengine.org/en/stable/community/contributing/updating_the_class_reference.html ](https://docs.godotengine.org/en/latest/tutorials/plugins/editor/inspector_plugins.html?highlight=inspector%20plugin)