Back out D66829458 ("hg backout D66771843 and D66770494")

Summary:
Original commit changeset: 80600946b0f4

Original Phabricator Diff: D66829458

#buildall

Reviewed By: yoney, ahilger

Differential Revision: D66848424

fbshipit-source-id: 3a28ac4ef4058a04269b45f54b1e7b152838d649

fb303/thrift/BUCK

@@ -46,7 +46,11 @@ thrift_library(
     thrift_cpp2_options = "frozen2,reflection",
     thrift_java_swift_options = ["deprecated_allow_leagcy_reflection_client"],
     thrift_js_options = ["node"],
-    thrift_python_options = ["experimental_generate_mutable_types"],
+    # DO_BEFORE(aristidis, 20250130): Remove experimental flags after launch.
+    thrift_python_options = [
+        "experimental_generate_mutable_types",
+        "experimental_generate_abstract_types",
+    ],
     thrift_rust_options = [
         "deprecated_default_enum_min_i32",
         "serde",