Add a way to debug rules

[quasilyte]

It's especially important to have a mechanism to debug how the rule is being executed, what types submatches have, etc.

Suppose we have a rule file like this:

package gorules
import "github.com/quasilyte/go-ruleguard/dsl/fluent"
func unslice(m fluent.Matcher) {
  m.Match(`$s[:]`).Where(m["s"].Type.Is(`string`)).Suggest(`$s`)
}

And a test Go file like this:

package example

func f(s string, a [10]int, b []byte) {
  _ = a[:] // no match
  _ = b[:] // no match
  _ = s[1:] // no match
  _ = s[:] // match
}

Debug output could look like:

$ ruleguard -debug-group unslice -rules rules.go example.go 
example.go:4: rejected ($s type filter)
  $s [10]int: a
example.go:5: rejected ($s type filter)
  $s []byte: b
example.go:7:6: suggestion: s

---

package gorules

import "github.com/quasilyte/go-ruleguard/dsl/fluent"

func gocriticArgOrder(m fluent.Matcher) {
	m.Match(`strings.HasPrefix($s1, $s2)`).
		Where(m["s1"].Const && !m["s2"].Const).
		Suggest(`strings.HasPrefix($s2, $s1)`)
}

package example

import "strings"

func _(v1, v2 string) {
	strings.HasPrefix("", "")
	strings.HasPrefix(v1, v2)
	strings.HasPrefix("", v2)
	strings.HasPrefix(v1, "")
}

$ ruleguard -debug-group gocriticArgOrder -rules rules2.go example2.go 
example2.go:6: rejected ($s2 is const)
  $s1 string: ""
  $s2 string: ""
example2.go:7: rejected ($s1 is not const)
  $s1 string: v1
  $s2 string: v2
example2.go:9: rejected ($s2 is const)
  $s1 string: v1
  $s2 string: ""
example2.go:8:2: suggestion: strings.HasPrefix(v2, "")