php.buildEnv: Automatically include extension dependencies
php.buildEnv: Automatically include extension dependencies

Some extensions depend on other extensions. Previously, these had to
be added manually to the list of included extensions, or we got a
cryptic error message pointing to strings-with-deps.nix, which wasn't
very helpful. This makes sure all required extensions are included in
the set from which textClosureList chooses its snippets.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs