ext/xml: Refactor extension to use FCC instead of zvals for handlers (#12340)

To get proper errors and sensible behaviour, as the current behaviour is somewhat insane and part of it should b

ext/xml: Refactor extension to use FCC instead of zvals for handlers (#12340)

To get proper errors and sensible behaviour, as the current behaviour is somewhat insane and part of it should be axed ASAP.

The behaviour is mostly intact with some minor BC breaks which are mentioned in UPGRADING.

Co-authored-by: Niels Dossche <7771979+nielsdos@users.noreply.github.com>

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