Add export type BlobInfo

When using images_upload_handler functionality, blobInfo needs to be passed as an argument as stated in the example bellow: const example_image_upload_handler = (blobInfo, progress) ...

The type of this argument is BlobInfo, but this is not exported from tinymce.

Instead of having to create a personalized interface that might not be updated in the future, or use a type 'any', it would be a good feature to have this type exported from tinymce.