Introduce new hook UploadVerifyUpload to allow preventing file uploads

Introduce new hook UploadVerifyUpload to allow preventing file uploads

The new hook runs at the beginning of UploadBase::performUpload().
Unlike the existing UploadVerifyFile hook, the new one provides the
information about the file description page being created, and the
user who is performing the upload. It also does not run for uploads
to stash.

The action=upload API and Special:Upload have been changed to treat
errors from UploadBase::performUpload() as recoverable, which means
that they will attempt to stash the file (previously they would require
the user to upload it again). This is mostly intended for errors from
the new hook, but I think it makes sense for the existing ones, which
are mostly transient filesystem erorrs.

Bug: T89302
Change-Id: Ie68801b307de8456e1753ba54a29c34c8063bc36