[Swift] Moves VTs from enums to structs to prevent empty enum generation

Moves VTs from enums to structs to prevent empty enum generation, which would usually cause a compilation error.

scripts/generate_code.py

@@ -517,6 +517,13 @@ flatc(
     cwd=swift_code_gen,
 )
 
+flatc(
+    SWIFT_OPTS_CODE_GEN + BASE_OPTS,
+    schema="empty_vtable.fbs",
+    cwd=swift_code_gen,
+    prefix="../../Tests/Flatbuffers/",
+)
+
 # Swift Wasm Tests
 swift_Wasm_prefix = "swift/Wasm.tests/Tests/FlatBuffers.Test.Swift.WasmTests"
 flatc(