Rename `.maintenance` for compatibility

[dd32]

FTP Servers really don't like hidden files, often due to the server being configured to hide them. This has caused compatibility issues such as #28013 & #34976

We should consider changing it to a non-hidden file, initial suggestion would be something such as wordpress.maintenance or wp.maintenance.

This would benefit us in that we'd no longer be creating/altering hidden files which are often treated as special by the system, which would make our upgrades more reliable.

[jdgrimes]

Note that we'll probably need to maintain back-compat for plugins that use the .maintenance file to send WordPress into maintenance mode. So we could add recognition of the new file and start using it for core's upgrade routines, but we'll probably want to keep the check for the old maintenance file as well.

[dd32]

Keeping backwards compat here is kind of annoying honestly, but would have to be done for a short period at least. I'd probably recommend supporting both at first and removing it in x.y+2

[chacha102]

Because of how often the check is ran, and because the file system doesn't cache false responses to file_exists, I definitely agree we should move to get rid of the backwards compatibility as soon as possible. Fortunately, for the majority of requests I only had to add one file_exists check.

I played around with a structure to store which of the file_exists checks came out true so that including the file didn't require an additional (albeit duplicate) check, but I felt that would ad to much overhead to the first set of checks that are much more commonly ran.

[voldemortensen]

For my own reference: ​https://github.com/bluehost/wp-tools/issues/6

[dd32]

Pushing to Future Release as beta hit.

[dd32]

Tempted to mark this as wonftix. I no longer really see it worthwhile to switch with reports of this being so few and far between.

Alternate options would be to use file_exists() directly and perform a FTP DELETE operation regardless of if we can see it via FTP.

[dd32]

Closing due to the lack of reports in recent history.