fix(windows): ensure DLLs can always be located by PHP (#2227)
Prevent crashes when `php.ini` references PHP extensions using relative
paths, and FrankenPHP is started from a different working directory than
the one containing extensions, or with `caddy start` (instead of `caddy
run`).
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>