When changing the directory name, automatically change the corresponding package name in the dart code

[rs5173]

In the current version, if you change the directory name, you need to manually change the dart code, which is very tedious

[stevemessick]

@scheglov are you still working on refactoring? If not, do you know who is?

[scheglov]

I think @jwren restored Move File refactoring partially, but we don't support renaming directories. I still have general interest in implementing refactorings, but did not have time recently.