refactor: replace Style.loadURL then/catch with await/catch

Author: kikuomax

src/style/style.ts

@@ -429,15 +429,16 @@ export class Style extends Evented {
         const request = await this.map._requestManager.transformRequest(url, ResourceType.Style);
         this._loadStyleRequest = new AbortController();
         const abortController = this._loadStyleRequest;
-        getJSON<StyleSpecification>(request, this._loadStyleRequest).then((response) => {
+        try {
+            const response = await getJSON<StyleSpecification>(request, this._loadStyleRequest);
             this._loadStyleRequest = null;
             this._load(response.data, options, previousStyle);
-        }).catch((error) => {
+        } catch (error) {
             this._loadStyleRequest = null;
             if (error && !abortController.signal.aborted) { // ignore abort
                 this.fire(new ErrorEvent(error));
             }
-        });
+        }
     }
 
     loadJSON(json: StyleSpecification, options: StyleSetterOptions & StyleSwapOptions = {}, previousStyle?: StyleSpecification) {