Generated Flow type files should have `// @flow strict` pragma

Currently, if the generated files with Flow types have `/* @flow */` at the top of the file.

This should be changed to `// @flow strict` so that the types can be imported in other `strict` files without warning.

Thanks!

Inspect the generator entry point that emits Flow-typed files and locate where the /* @flow */ header is produced. Change the generated pragma to // @flow strict, then verify the generated files can be imported by strict Flow files without warnings.

Written by the indexing model from the issue text.