This fixes cases where pre-rotation wasn't occuring when glClear() was
implemented by a small shader.  A specialized viewport was generated
(thus, not with ContextVk::updateViewport()) for the entire
framebuffer.  However, the framebuffer width and height were not
swapped for 90/270-degree rotation cases, and so the wrong viewport.y
value was calculated.

Test: angle_deqp_gles2_tests --gtest_filter=dEQP.GLES2/functional_color_clear*
Bug: b/157933235
Bug: b/157933198
Change-Id: I1ac158c84ef812c8863dee01c6c8bfe9295b900e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2231597Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>