Support toggle on smoothness texture later; don't enable smoothness texture feature when creating a mesh-terrain or converting a terrain.

[zwcloud]

• [x] single mesh-terrain conversion/creation zwcloud/MeshTerrainEditor@5f926d10002fbb036ea64a7b01e0c30e86cc2a9a
• [x] multiple mesh-terrains conversion/creation
• [x] implement TileContainerEditor for easier tiled mesh-terrains support of albedo&smoothness textures

[zwcloud]

Done before https://github.com/zwcloud/MeshTerrainEditor/commit/a2ecda20c50ae87bf3a37d378ab8beba2e01cde4