[IMP] survey: improve survey form navigation

This commit slightly changes the way users navigate through the survey form:
- The back button was moved to the bottom-right of the screen.
- The "Continue" button stays at the center but there is also a "next" button
  at the bottom-right of the screen (same behavior -> submits the form)
- Arrow keys (left + right) navigation is now supported

Technical note: As the survey navigation is now outside of the survey content,
that was re-rendered on every submit, we have to manually refresh the
navigation with a second template render on the controller side.

LINKS

PR #46768
Task 2208574