fix：fitExtent方法，增加isFraction参数，增加定位支持小数zoom (#2048)

Co-authored-by: l2458 <liuxc2458@dtdream.com>

src/map/Map.js

@@ -1026,14 +1026,15 @@ class Map extends Handlerable(Eventable(Renderable(Class))) {
      * @param  {Number} [options.paddingTop] - Sets the amount of padding in the top of a map container
      * @param  {Number} [options.paddingRight] - Sets the amount of padding in the right of a map container
      * @param  {Number} [options.paddingBottom] - Sets the amount of padding in the bottom of a map container
+	 * @param  {Boolean} [options.isFraction=false] - can locate to fractional zoom
      * @return {Map} - this
      */
     fitExtent(extent, zoomOffset, options = {}, step) {
         if (!extent) {
             return this;
         }
         extent = new Extent(extent, this.getProjection());
-        const zoom = this.getFitZoom(extent, false, options) + (zoomOffset || 0);
+        const zoom = this.getFitZoom(extent, options.isFraction || false, options) + (zoomOffset || 0);
         let center = extent.getCenter();
         if (this._getPaddingSize(options)) {
             center = this._getCenterByPadding(center, zoom, options);