bug(#3481): builds FQN via XSL

[maxonfjvipon]

Ref: #3481

In this PR I introduced XSL transformation that finds closest objects references and builds FQN, almost the same as add-refs.xsl does, but it inserts explicit objects.

Consider the next EO from builds-fnq.yaml pack:

# No comments.
[x y] > first
  stdout x > std
  [std] > second
    std x > inner
    [] > third
      5 > x
      x.plus y > sum
      std qwe > closest
    [] > fourth
      "some" > inner
      ^.inner > outer
      inner > self
foo > bar

# Foo.
[] > foo

The transformation converts it to the next EO:

[x y] > first
  stdout $.x > std
  [std] > second
    $.std ^.x > inner
    [] > third
      5 > x
      $.x.plus ^.^.y > sum
      ^.std qwe > closest
    [] > fourth
      "some" > inner
      ^.inner > outer
      $.inner > self
foo > bar

# Foo.
[] > foo

As you may see - it adds necessary $ or ^. objects.

When it's used in TrShaking - we're not going to need add-refs.xsl (which is used a several times) anymore because we're going to have FQN that are not needed be be resolved.

UPD:
If future, if the transformation is going to be heavy, it can be easily simplified: instead of inserting objects directly - we can attach some numeric attribute to target object. If attribute value is 0 - it means we should use $, if it's > 0 then we should insert some ^. objects. How much - attribute value shows

[maxonfjvipon]

@yegor256 please check

[yegor256]

@maxonfjvipon looks cool!