WIP: flow type tooling

What does this MR do?

adds flow type checking add sample file with basic annotations

Are there points in the code the reviewer needs to double check?

• breaks codeclimate & static check, need to add plugin
• doesn't work in .vue files without gross comment hacks :( https://github.com/facebook/flow/issues/2691

Why was this MR needed?

Maybe it isn't..

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• [ ] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29132 (moved)