Modification for PR based on comment

apply(node: Node): Unit -> apply(node: Node) = ???
AstCompressor: removal of unused import
AstTag -> NodeTag
Removal of extra empty lines in AstNode
Removal of unused one-liner
AstNode.scala -> Node.scala
Implicits.scala -> Enrichments.scala
ListTakeAndSplit -> RichList
Nil for selections in the recomposed tree
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