Merge pull request #15544 from Automattic/vkarpov15/base-type

types(connection): add `base` to connection type

Author: vkarpov15

types/connection.d.ts

@@ -72,11 +72,15 @@ declare module 'mongoose' {
   }[keyof SchemaMap];
 
   class Connection extends events.EventEmitter implements SessionStarter {
+    /** Runs a [db-level aggregate()](https://www.mongodb.com/docs/manual/reference/method/db.aggregate/) on this connection's underlying `db` */
     aggregate<ResultType = unknown>(pipeline?: PipelineStage[] | null, options?: AggregateOptions): Aggregate<Array<ResultType>>;
 
     /** Returns a promise that resolves when this connection successfully connects to MongoDB */
     asPromise(): Promise<this>;
 
+    /** The Mongoose instance this connection is associated with */
+    base: Mongoose;
+
     bulkWrite<TSchemaMap extends Record<string, AnyObject>>(
       ops: Array<ConnectionBulkWriteModel<TSchemaMap>>,
       options: mongodb.ClientBulkWriteOptions & { ordered: false }