`excessive-visibility` lint doesn't flag unused public methods

[yegor256]

Consider this object:

[t] > phrase
  pos.gte 0 > multi-words
  t.index-of " " > pos

  (book "Object Thinking").multi-words ++> can-find-space-in-name

Here, the pos is not used by any tests. It can and should be made private:

[t] > phrase
  pos.gte 0 > multi-words
  t.index-of " " >> pos
                ^^^^
                here

Let's create a lint that would catch this. If no tests refer to a method, it must be private/obfuscated (>>).

[aryansk]

I’m taking the narrow excessive-visibility lint proposal and adding focused XSL fixture coverage for a public method that no unit test references, plus the allowed control case.