Allow passing multiple FeatureOptions to `required:`

Passing multiple `FeatureOption` objects will do an `AND` on them all, f.ex.:

```meson
gtk_x11_dep = dependency('gtk+-x11-3.0', version : '>= 3.10',
required : [get_option('x11'), get_option('gtk3')])
```
The table looks like:

| A | B | A & B |
|---|---|-------|
| enabled | enabled | enabled |
| enabled | disabled | disabled |
| enabled | auto | auto |
| disabled | disabled | disabled |
| disabled | auto | disabled |
| auto | auto | auto |

The only interesting case in this is when A is `enabled` and B is `auto`. I believe that the more useful behaviour in that case is to evaluate to `auto` for the dependency.