Add bookworm- and trixie-based dev images for PHP 8.5 development
Per Krinkle, for the bookworm-based images this installs PHP from component/php85 in the Wikimedia APT repository rather than from Sury, so that these images stay near to the production ones.
For trixie, Wikimedia doesn't yet have these packages, so I went with the old model of using the packages from Sury; we should switch these once PHP 8.5 is Wikimedia-packaged.
php-ast isn't provided by Wikimedia in any PHP or OS version, so we keep Sury around for the bookworm images anyway.