Test shader builtin accessibility from different stages Test that fragment, vertex or compute shader exclusive builtins are not accessible from another shader stage. This will protect against regressions when refactoring the symbol table. BUG=angleproject:2267 TEST=angle_unittests Change-Id: I50f97cbde3f1c5cb4584568e3008f1dab724b769 Reviewed-on: https://chromium-review.googlesource.com/941953 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>