Try to make POSTs as transactional as possible

Try to make POSTs as transactional as possible

* WMF has has ignore_user_abort() for *all* request in configuration
  for many years. This brings this to default MediaWiki for all POST
  requests, which are likely to do writes. Of course, some do not,
  notably parse requests and previews, since GET cannot carry the
  payload. Avoiding data corruption is more important though.

Bug: T102890
Change-Id: I11c8b0d99583a682f756cef9747ec5ba9751c5e3