Now that ternary nodes are not represented by TIntermSelection any
more, TIntermIfElse is an easier name to understand for newcomers to
the code.

BUG=angleproject:1490
TEST=angle_unittests

Change-Id: Ia1e04e356ab93409400245092a84533d7dfd129d
Reviewed-on: https://chromium-review.googlesource.com/385416Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>