This way we can query the brush types, e.g. to filter out eraser brushes in the brush asset selector while the eraser tool is selected, see https://projects.blender.org/blender/blender/issues/126032. Technically a brush may have different brush types depending on the mode. So we store a type for all supported modes. Ideally the name of the custom metadata property would match the name of the properties in RNA. They will match after #126796, the names here are the new ones, to avoid having to version asset metadata. Pull Request: https://projects.blender.org/blender/blender/pulls/124618