Attribute Macro spirv_recursive_for_testing

#[spirv_recursive_for_testing]

For testing only! Is not reexported in spirv-std, but reachable via spirv_std::macros::spirv_recursive_for_testing.

May be more expensive than plain spirv, since we’re checking a lot more symbols. So I’ve opted to have this be a separate macro, instead of modifying the standard spirv one.