refactor(TeacherProjectService): Move branch authoring code

- In TeacherProjectService, move these code to NodeAdvancedBranchAuthoringComponent, where it's actually being called
   - setTransitionLogicField()
   - setTransition()
   - addBranchPathTakenConstraints()
- Remove TeacherProjectService.isNodeIdUsed() since it's unused
- Add private keyword and function return types in surrounding code