DEV: Change uploads.filesize column to bigint (PR #14334)

This is necessary to allow for large file uploads via the direct S3 upload mechanism, as we convert the external file to an Upload record via ExternalUploadManager once it is complete.

This will allow for files larger than 2,147,483,647 bytes (2.14GB) to be referenced in the uploads table.

This is a table locking migration, but since it is not as highly trafficked as posts, topics, or users, the disruption should be minimal.