partial eval: support negated expressions with support rules

[tsandall]

Today, negated expressions are not partially evaluated; the plugged expression is saved and partial evaluation continues in the current query.

In some cases, it's advantageous to partially evaluate negated expressions and produce support rules.

Example

Query:

x = 1; not p[x]

Policy:

p[x] {
  input.a = y
  x = r[y]
}

r = {"foo": 0, "bar": 1, "baz": 2}

Result:

x = 1; not support.p[1]

Support:

package support

p[1] {
  input.a = "bar"
}