Swift: cleanup and some docstrings for codegen

Also added code generation and clang formatting to the pre-commit
configuration.

swift/ql/lib/swift.dbscheme

@@ -8,6 +8,10 @@ sourceLocationPrefix(
   string prefix: string ref
 );
 
+answer_to_life_the_universe_and_everything(
+   int answer: int ref
+)
+
 
 // from codegen/schema.yml