Refactor unary operation constant folding code This change splits TIntermConstantUnion::foldUnary into two functions: - foldUnaryWithDifferentReturnType: - Handles constant folding of operations where the return type has a different number of components compared to the operand type. - foldUnaryWithSameReturnType: - Handles constant folding of unary operations where the return type is the same as operand type. BUG=angleproject:913 TEST=angle_unittests, dEQP Tests (dEQP-GLES3.functional.shaders.constant_expressions.builtin_functions.*) Change-Id: I675891138d4e17fd2390c03e9f710e0be0b7c7b6 Reviewed-on: https://chromium-review.googlesource.com/283464 Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>