Type and refactor moveSpecifiers helper

[thatblindgeye]

From comments left on #808, we should type and possibly refactor the moveSpecifiers helper. Reason for refactoring it would be that it may make it easier to implement types, but also because right now it cannot be used inline (e.g. call the helper as part of some other logic) -- it has to be the only logic for a codemod due to it being passed to the create method that gets exported from a codemod file.