Rotate selections: Adjacent selections are merged when rotating an empty text into one of them

[p-e-w]

Note that due to the way selections work in Atom, this cannot be fixed without introducing global state.

Test

<|a|><|a|> <||>a
---
does not merge adjacent selections when rotating an empty text into one of them
---
envy:rotate-selections-forward
envy:rotate-selections-forward
envy:rotate-selections-forward
---
<|a|><|a|> <||>a
---