solr-client: Add searchAsync to Client interface (#40143)

* solr-client: Add searchAsync to Client interface

* Updated searchAsync return value to object

* Fixed whitespace

types/solr-client/index.d.ts

@@ -161,6 +161,7 @@ export interface Client {
     escapeSpecialChars(s: string): string;
     query(): Query;
     atomicUpdate(doc: object, callback?: (err: Error, data: object) => void): ClientRequest;
+    searchAsync(query: Query): Promise<object>;
 }
 
 export as namespace Solr;