Return type of Folder#createDialog is documented incorrectly

[aaclayton]

Originally in GitLab by @ghost91-

Environment Details

• Foundry VTT Version: v9.245

Issue Description

In v9.245, Folder#createDialog was adjusted so that it returns the created document (or null if the FolderConfig is closed), which brings it in line with how ClientDocumentMixin#createDialog works (thanks for that!). However, it looks like the documentation was not adjusted accordingly. It still reads as follows:

   * @return {Application}      An active FolderConfig instance for creating the new Folder document

It should be adjusted to match the new (correct) behavior.