Add new assist to remove dbg!() calls

Add new assist to remove dbg!() calls

This fixes #758.

Currently we try to maintain the cursor position relative to the statement under
cursor, if the cursor is inside the dbg! macro call.

Meaning:

let foo = dbg!(some.complex<|>().expression());

Should turn into:

let foo = some.complex<|>().expression();

With the cursor staying in place.