Interface blocks were mistakenly being allowed in some types of unary,
binary and ternary expressions, when they should not have been.

BUG=angleproject:2030
TEST=angle_unittests

Change-Id: Ie75833ee208e1b7fef8f77fa91b90da278bc6498
Reviewed-on: https://chromium-review.googlesource.com/500269Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>