chore(tsickle): add @Annotation annotations

This lets users continue using runtime-sideeffect Decorators if they choose,
only down-leveling the marked ones to Annotations.

Also remove the "skipTemplateCodegen" option, which is no longer needed
since Angular compiles with tsc-wrapped rather than ngc. The former doesn't
include any codegen.

modules/@angular/compiler/test/offline_compiler_util.ts

@@ -71,4 +71,4 @@ export class SimpleJsImportGenerator implements ImportGenerator {
       return importedUrlStr;
     }
   }
-}
+}