From PHP 8.4, `xml_set_object()`, and passing a string helper to
`xml_set_.*_handler()` has been deprecated.
This commit updates all uses of these in core code.
Please note the following libraries have not been modified and will be
handled via library upgrades separately:
- simplepie
- phpxmlrpc
- tcpdf
In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.
1. Changes progress bar code to allow headings for progress bar (so users have
some clue what's going on if a page has more than one progress bar).
2. Changes restore code so that a progress bar can display during pre-checks if
they take longer than 5 seconds.
3. Changes pre-check and restore code so that, in various points where the system
can take a long time within an individual step, intederminate progress is
indicated and it won't time out.
Andrew Nicols