Currently, Naga does not require the subgroups extension be declared in order to use subgroup functionality, in fact, Naga was intentionally made to reject shaders declaring the subgroups extension (#7474) because our subgroup support is not spec-complete (see #5555).

This means that wgpu native clients using Features::SUBGROUP_* must not be declaring the subgroups extension in their shaders, which will become a compatibility issue if we later change naga to require it.