ESSL specs only allow a limited number of operators on arrays and
structs. The spec section on the ternary operator contradicts this to an
extent, saying that the second and third operands can be "any type" or
"any type other than an array", but we interpret the spec so that the
operator restrictions on structures and arrays override this.

BUG=angleproject:976
TEST=angle_unittests

Change-Id: Icd90d5450dcb94bb23b1683d4cb9e579e82de4ad
Reviewed-on: https://chromium-review.googlesource.com/265644Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>