refactor(TeacherProjectService): Move branch authoring code

[hirokiterashima]

Changes

• In TeacherProjectService, move these functions to NodeAdvancedBranchAuthoringComponent, where they're actually being called
  • setTransitionLogicField()
  • setTransition()
  • addBranchPathTakenConstraints()
• Remove TeacherProjectService.isNodeIdUsed() since it's unused
• Use nullish coalescence (??) in ProjectService.instantiateDefaults()
• Add private keyword and function return types in surrounding code

Test

• Node branch authoring works as before (e.g. creates correct transitions and constraints)
• Unit loads as before in VLE, CM, AT (to test ProjectService.instantiateDefaults())

Closes #1220