add MouseMode constant

modules/option/index.js

  * @Date: 2020-03-05 22:00:17
  */
 
+export { default as MouseMode } from './MouseMode'
 export { default as ViewerOption } from './ViewerOption'
 export { default as CameraOption } from './CameraOption'

packages/core/src/components.js

 import { Util, DomUtil, PlotUtil } from '@dc-modules/utils'
 import { Transform, CoordTransform } from '@dc-modules/transform'
 import { MouseEventType, SceneEventType } from '@dc-modules/event'
+import { MouseMode } from '@dc-modules/option'
 import {
   area,
   bounds,
   CoordTransform,
   MouseEventType,
   SceneEventType,
+  MouseMode,
   Math: Cesium.Math,
   Viewer,
   World: Viewer,