Incorrect dead code removal quick fix when multiple cases share a body

[stereotype441]

The following code triggers the unreachable_switch_case hint:

enum E { e1, e2 }

_f(E e) {
  switch (e) {
    case E.e1:
    case E.e2:
    case E.e1: // hint shown here
      print('hello');
  }
}

That's behaving as expected. However, if I go to the location where the hint is reported, and invoke the "remove dead code" quick fix, the code is changed to:

enum E { e1, e2 }

_f(E e) {
  switch (e) {
    case E.e1:
    case E.e2:
  }
}

Which is not equivalent. The print('hello'); line shouldn't have been deleted, because it is not dead; only the extraneous case E.e1 is dead.

[stereotype441]

I'm going to work on this, since otherwise it will block my ability to roll out a fix to #54575.