lib/types: maybeRaw should propagate elemType's sub-options

[MattSturgeon]

This is technically redundant, because we patch either to be recursive. But I think it is best if maybeRaw does this explicitly, without relying on that behaviour.

[MattSturgeon]

error: A definition for option `plugins.cmp.settings.sources' is not of type `list of (attribute set of anything)'. Definition values:
- In `/nix/store/a9v1l0scrw2nmsp7k40kywijf78mns6s-test-sources/plugins/cmp/default.nix':
    {
      __raw = ''
        cmp.config.sources({
          {
            {name = "path"},
    ...

I have no idea how this change could trigger that though...

[MattSturgeon]

I think a proper substSubModules is a little more complex than just re-using the elem-type's