with: attempt to simplify

[tomberek]

Reduces Nixpkgs diff by 10%.
With this and a few pending PRs:
24157 files changed, 1562119 insertions(+), 974518 deletions(-)

[kamadorueda]

Not too far from the right implementation

[kamadorueda]

The test that this does not pass is:

with xx; 
#comment 
expression

Because it will become:

with xx; 
#comment expression

There are a few examples in other rules on how to deal with this, basically you check if the previous thing was a comment, and if so, newline+pad, otherwise whitespace