Migrate spec/javascripts/droplab/ to Jest

Description

Let's migrate the specs in spec/javascripts/droplab/ from Karma to Jest.

See the related epic for how to do this.

• spec/javascripts/droplab/plugins/input_setter_spec.js !32757 (merged)
• spec/javascripts/droplab/drop_down_spec.js !32765 (merged)
• spec/javascripts/droplab/hook_spec.js !32764 (merged)