Add Serialize/Deserialize for Dynamic and ImmutableString.

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
         os: [ubuntu-latest]
         flags:
           - ""
-          - "--features serde,internals"
+          - "--features metadata,internals"
           - "--features unchecked"
           - "--features sync"
           - "--features no_optimize"
@@ -32,7 +32,7 @@ jobs:
           - "--features no_module"
           - "--features no_closure"
           - "--features unicode-xid-ident"
-          - "--features sync,no_function,no_float,no_optimize,no_module,no_closure,serde,unchecked"
+          - "--features sync,no_function,no_float,no_optimize,no_module,no_closure,metadata,unchecked"
         toolchain: [stable]
         experimental: [false]
         include: