Add resources.GetRemote

In Hugo 0.89 we added remote support to `resources.Get`.

In hindsight that was not a great idea, as a poll from many Hugo users showed. See Issue #9285 for more details.

After this commit `resources.Get` only supports local resource lookups. If you want to support both, you need to use a construct similar to:

Also improve some option case handling.

```
{{ resource := "" }}
{{ if (urls.Parse $url).IsAbs }}
{{ $resource = resources.GetRemote $url }}
{{ else }}
{{ $resource = resources.Get $url }}
{{ end }}
```

Fixes #9285
Fixes #9296

tpl/internal/go_templates/texttemplate/exec.go

@@ -783,6 +783,8 @@ func (s *state) validateType(value reflect.Value, typ reflect.Type) reflect.Valu
 			}
 		case reflect.PtrTo(value.Type()).AssignableTo(typ) && value.CanAddr():
 			value = value.Addr()
+		case value.IsZero():
+			s.errorf("got <nil>, expected %s", typ)
 		default:
 			s.errorf("wrong type for value; expected %s; got %s", typ, value.Type())
 		}