At the moment, inserting a new line while being in a comment result in a
"//<indentation>" instead of "<indentation>//".
To fix this, we just re-order both InsertChar hooks.
`x` is often criticized as hard to predict due to its slightly complex
behaviour of selecting next line if the current one is fully selected.
Change `x` to use the previous `<a-x>` behaviour, and change `<a-x>` to
trim to fully selected lines as `<a-X>` did.
Adapt existing indentation script to the new behaviour
