Optimize some usages of double unary operators in suggestions

When an expression is made of a `!` or `-` unary operator which does not
change the type of the expression, use a new variant in `Sugg` to denote
it. This allows replacing an extra application of the same operator by
the removal of the original operator instead.

Also, when adding a unary operator to a suggestion, do not enclose the
operator argument in parentheses if it starts with a unary operator
itself unless it is a binary operation (including `as`), because in this
case parentheses are required to not bind the lhs only.

Some suggestions will now be shown as `x` instead of `!!x`. Right now,
no suggestion seems to produce `--x`.

0 files changed, 0 insertions, 0 deletions