Move AST transformations to a subdirectory Move AST transformations to compiler/translator/tree_ops. BUG=angleproject:2409 TEST=angle_unittests Change-Id: I9c620e98707d22d005da6192fe7d1b4e8030aadd Reviewed-on: https://chromium-review.googlesource.com/975550 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>