feat: add types for the result of bulk initialize methods (#2654)

NODE-2932

Author: mbroadst

src/collection.ts

@@ -1305,12 +1305,12 @@ export class Collection implements OperationParent {
   }
 
   /** Initiate an Out of order batch write operation. All operations will be buffered into insert/update/remove commands executed out of order. */
-  initializeUnorderedBulkOp(options?: BulkWriteOptions): any {
+  initializeUnorderedBulkOp(options?: BulkWriteOptions): UnorderedBulkOperation {
     return new UnorderedBulkOperation(this, resolveOptions(this, options));
   }
 
   /** Initiate an In order bulk write operation. Operations will be serially executed in the order they are added, creating a new operation for each switch in types. */
-  initializeOrderedBulkOp(options?: BulkWriteOptions): any {
+  initializeOrderedBulkOp(options?: BulkWriteOptions): OrderedBulkOperation {
     return new OrderedBulkOperation(this, resolveOptions(this, options));
   }