Disable mesh compression if vertex position.z is always 0

[jsjtxietian]

Fixes #85963

As #85963 (comment) mentioned, "We could detect if the z channel is used in the vertex positions, if z is always 0, we could assume the mesh is 2D and disable compression" , this pr is a brute-force way of implementing it. I'm not sure if it's the right place to insert this check, but it seems the suitable place.

Feel free to correct me!

[fire]

Is it true that a lot of the code assumes mesh compression is on? I am not that familiar.

[clayjohn]

The code looks good, but it should be in the respective importers, not in the SurfaceTool.

godot/editor/import/3d/resource_importer_obj.cpp

Lines 386 to 387 in 2e7fc81

	mesh_flags = 0;
	}

godot/modules/gltf/gltf_document.cpp

Lines 2825 to 2827 in 16d6142

	if (p_state->force_disable_compression || !a.has("POSITION") || !a.has("NORMAL") || p.has("targets") || (a.has("JOINTS_0") || a.has("JOINTS_1"))) {
	flags &= ~RS::ARRAY_FLAG_COMPRESS_ATTRIBUTES;
	}

godot/editor/import/3d/editor_import_collada.cpp

Lines 999 to 1002 in 16d6142

	if (p_mesh->get_blend_shape_count() != 0 || p_skin_controller) {
	// Can't compress if attributes missing or if using vertex weights.
	mesh_flags &= ~RS::ARRAY_FLAG_COMPRESS_ATTRIBUTES;
	}

[clayjohn]

Looks great! There is just a small typo in your comment. Once that is fixed, we can merge this for 4.3!

[clayjohn]

Looks great! Thank you

[akien-mga]

Thanks!