ref: migrate stream feedback flow to TypeScript

[karrui]

Problem

This PR migrates the god controller function for streamFeedback into the DDD architecture we all know and love.

In addition, also add AuthService#getFormAfterPermissionChecks helper function for the repetitive task steps of

1. Retrieving form
2. Checking form active state
3. Checking form permissions

There is also a cherry picked commit 3860e34 from #729 that adds exhaustive switch case typeguard.

Solution

Features:

• add AuthService#getFormAfterPermissionChecks helper function
• to that end, add adminFormUtils#getAssertPermissionFn factory that returns the appropriate function.
• add FeedbackSvc#getFormFeedbackStream fn
• add AdminFormCtl#handleStreamFormFeedback handler fn

Tests

The usual. No success test case for the controller since I still cannot figure out how to handle stream tests, and Google is not helping.

No integration tests yet since router is not migrated yet.