"Using GridMaps" tutorial is unclear and contains outdated info

[ash2x3zb9cy]

Your Godot version: stable (4.1)

Issue description:

• The sample project is an unconverted 3.x project, and opening it in 4.1 causes warnings.
• The names of nodes in the hierarchy shown in the image in the setion "NavigationMeshes" (meshlibrary_scene.png) do not match those in the sample project
• The section "Using GridMap" refers to the property "Theme" of GridMap, which was removed in 3.2 and should instead refer to "Mesh Library"
• The "NavigationMeshes" section is generally unclear and uninformative.

URL to the documentation page: https://docs.godotengine.org/en/stable/tutorials/3d/using_gridmaps.html

[pheather]

It would also be helpful to have an additional section regarding Mesh Library import functionality from the editor scene context bar interface (ref: Mesh Library Import from Scene (Apply Transformation) example)

[1337GameDev]

Looking at this tutorial as well, it doesn't take into account GLTF models (.glb) and how to handle those for making a MeshLibrary.

Drag+dropping a GLB into a scene you want to export as a mesh library generates a Node3D object, with no children
(as i'd assume it'd also include a MeshInstance as a child node).

Since GLB is the preferred format for models in Godot, this seems odd to not have more obvious support for them.