Feature Request: bake GridMap to MeshInstance

[MJacred]

As GridMap has all kinds of issues/drawbacks in actual use, it would be nice to be able to convert it into normal MeshInstance

probably need either GridMap's get_meshes or make_baked_meshes func, see: godotengine/godot#46130 (comment)

I imagine 4 variants are needed

1. take whole GridMap and convert it into 1 MeshInstance per Mesh
2. take whole GridMap and convert it into one single MeshInstance (requires merging meshes)
3.-4. create a selection (using selection via SHIFT key + mouse drag) -> then merge selected elements like in 1. or 2.

plus optional whitelist and blacklist of specific mesh parts of your mesh library (but that can come in the next iteration)

Although, using an Area3D for merging would be better, because you could do multiple "selections" for fine control