Add explanation of purpose and usecase between MeshInstance2D and Polygon2D in a 2D mesh workflow

[golddotasksquestions]

Your Godot version: Godot 3.4.4, Godot

Issue description: This tutorial about 2D Meshes in Godot is pretty good, however is does not mention why I would use a MeshInstance2D over a Polygon2D or vice-versa. Both seem to have a very similar workflow (using the converter in the Sprite toolbar), and I would assume similar benefits.

Also the graphic need to be updated. In particular this one: https://docs.godotengine.org/en/latest/_images/mesh2d2.png

This is not a documentation issue, but I suppose the naming should be changed to "Convert to Meshinstance2D" instead of "Mesh2D", since the Mesh2D does not actually exist.

URL to the documentation page (if already existing): https://docs.godotengine.org/en/stable/tutorials/2d/2d_meshes.html https://docs.godotengine.org/en/latest/tutorials/2d/2d_meshes.html

[Calinou]

This is not a documentation issue, but I suppose the naming should be changed to "Convert to Meshinstance2D" instead of "Mesh2D", since the Mesh2D does not actually exist.

This is already fixed in master, but the class reference hasn't been updated to follow.

I don't know the exact use case differences between Polygon2D and MeshInstance2D, but Polygon2D is more general-purpose whereas MeshInstance2D should be reserved to special uses only.