add gpx layer

modules/layer/index.js

 export { default as DynamicLayer } from './type/DynamicLayer'
 export { default as FeatureGridLayer } from './type/FeatureGridLayer'
 export { default as GeoJsonLayer } from './type/GeoJsonLayer'
+export { default as GpxLayer } from './type/GpxLayer'
 export { default as GroundPrimitiveLayer } from './type/GroundPrimitiveLayer'
 export { default as HtmlLayer } from './type/HtmlLayer'
 export { default as KmlLayer } from './type/KmlLayer'

modules/layer/type/GpxLayer.js

+/**
+ * @Author: Caven
+ * @Date: 2020-01-19 11:03:17
+ */
+
+import { Cesium } from '@dc-modules/namespace'
+import State from '@dc-modules/state/State'
+import Layer from '../Layer'
+
+class GpxLayer extends Layer {
+  constructor(id, url, options = {}) {
+    if (!url) {
+      throw new Error('GpxLayer: the url is empty')
+    }
+    super(id)
+    this._delegate = Cesium.KmlDataSource.load(url, options)
+    this._state = State.INITIALIZED
+  }
+
+  get type() {
+    return Layer.getLayerType('gpx')
+  }
+
+  set show(show) {
+    this._show = show
+    this._delegate &&
+      this._delegate.then(dataSource => {
+        dataSource.show = this._show
+      })
+  }
+
+  get show() {
+    return this._show
+  }
+
+  eachOverlay(method, context) {
+    if (this._delegate) {
+      this._delegate.then(dataSource => {
+        let entities = dataSource.entities.values
+        entities.forEach(item => {
+          method.call(context, item)
+        })
+      })
+      return this
+    }
+  }
+}
+
+Layer.registerType('gpx')
+
+export default GpxLayer

packages/core/src/components.js

   DynamicLayer,
   FeatureGridLayer,
   GeoJsonLayer,
+  GpxLayer,
   HtmlLayer,
   KmlLayer,
   LabelLayer,
   DynamicLayer,
   FeatureGridLayer,
   GeoJsonLayer,
+  GpxLayer,
   HtmlLayer,
   KmlLayer,
   LabelLayer,