Update to latest built_value (#222)

Also update build_runner and source_gen.

Manually hold back some changes in the generated files - some fields
were missing from `TypeReference`.

Author: natebosch

build.disabled.yaml

@@ -10,5 +10,5 @@ builders:
     builder_factories:
       - "builtValueBuilder"
     build_extensions:
-      ".dart": ".g.dart"
+      ".dart": [".g.dart"]
     build_to: "source"