CodeFormatter: One-line formatting and whitespace

[ldoblies]

One-line formatting gets messed up by unexpected whitespace placement in the syntax tree.

As of now, one-line formatting for certain nodes (e.g. a ReturnClause) is only applied if the
input is also on one line.
E.g.

if ($a) then $b else $c

is left as is, while

if ($a) then $b else
$c 

is formatted to

if ($a) then
  $b
else
  $c

because the input is not on one line.

WS in the AST after certain nodes messes this up, e.g.

for $i in (let, for)
return return

is formatted to

for $i in (let, for)
return
    return

because of a '\n' being part of the ReturnClause (it is unclear to me why this WS node is or should be a child of the ReturnClause). Could be fixed by removing WS that have no semantic impact from the end of nodes (and moving it to the parent node).