reify shouldn't unexpand macros

[scabug]

Firstly we can only undo tree transformations not the potential side-effects induced by macro implementations during the expansion.

Secondly (and more importantly from the practical point of view), when used as a quasiquoting facility, unexpanding reification will force nested macros to reexpand in a different lexical context, subverting hygiene.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6115?orig=1
Reporter: @xeno-by

[SethTisue]

closing all quasiquote tickets; see #10755

this isn't strictly a quasiquote-only ticket, but this stuff isn't really changing anymore. someone can comment and/or reopen if they disagree