Fixing #7479

Types converted:

- `NixStringContextElem`
- `OutputsSpec`
- `ExtendedOutputsSpec`
- `DerivationOutput`
- `DerivationType`

Existing ones mostly conforming the pattern cleaned up:

- `ContentAddressMethod`
- `ContentAddressWithReferences`

The `DerivationGoal::derivationType` field had a bogus initialization,
now caught, so I made it `std::optional`. I think #8829 can make it
non-optional again because it will ensure we always have the derivation
when we construct a `DerivationGoal`.

See that issue (#7479) for details on the general goal.

`git grep 'Raw::Raw'` indicates the two types I didn't yet convert
`DerivedPath` and `BuiltPath` (and their `Single` variants) . This is
because @roberth and I (can't find issue right now...) plan on reworking
them somewhat, so I didn't want to churn them more just yet.

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>

src/libstore/outputs-spec.cc

@@ -17,7 +17,7 @@ bool OutputsSpec::contains(const std::string & outputName) const
         [&](const OutputsSpec::Names & outputNames) {
             return outputNames.count(outputName) > 0;
         },
-    }, raw());
+    }, raw);
 }
 
 static std::string outputSpecRegexStr =
@@ -49,7 +49,7 @@ OutputsSpec OutputsSpec::parse(std::string_view s)
     std::optional spec = parseOpt(s);
     if (!spec)
         throw Error("invalid outputs specifier '%s'", s);
-    return *spec;
+    return std::move(*spec);
 }
 
 
@@ -85,7 +85,7 @@ std::string OutputsSpec::to_string() const
         [&](const OutputsSpec::Names & outputNames) -> std::string {
             return concatStringsSep(",", outputNames);
         },
-    }, raw());
+    }, raw);
 }
 
 
@@ -98,7 +98,7 @@ std::string ExtendedOutputsSpec::to_string() const
         [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> std::string {
             return "^" + outputSpec.to_string();
         },
-    }, raw());
+    }, raw);
 }
 
 
@@ -118,9 +118,9 @@ OutputsSpec OutputsSpec::union_(const OutputsSpec & that) const
                     ret.insert(thoseNames.begin(), thoseNames.end());
                     return ret;
                 },
-            }, that.raw());
+            }, that.raw);
         },
-    }, raw());
+    }, raw);
 }
 
 
@@ -142,9 +142,9 @@ bool OutputsSpec::isSubsetOf(const OutputsSpec & that) const
                             ret = false;
                     return ret;
                 },
-            }, raw());
+            }, raw);
         },
-    }, that.raw());
+    }, that.raw);
 }
 
 }
@@ -169,7 +169,7 @@ void adl_serializer<OutputsSpec>::to_json(json & json, OutputsSpec t) {
         [&](const OutputsSpec::Names & names) {
             json = names;
         },
-    }, t.raw());
+    }, t.raw);
 }
 
 
@@ -189,7 +189,7 @@ void adl_serializer<ExtendedOutputsSpec>::to_json(json & json, ExtendedOutputsSp
         [&](const ExtendedOutputsSpec::Explicit & e) {
             adl_serializer<OutputsSpec>::to_json(json, e);
         },
-    }, t.raw());
+    }, t.raw);
 }
 
 }