Adding meta-pkgs/bulk-test-php.

As suggested by gdt@ in [1], create a meta-pkg that would allow for
rapid regression testing of PHP version changes, at least in terms
of build.

Lightly inspired from the ones of Go and Rust. Feel free to modify
and adapt it.

[1] https://mail-index.netbsd.org/tech-pkg/2023/11/13/msg028414.html

(jym)