Enable all multiview rendering tests for layered framebuffers
Enable all multiview rendering tests for layered framebuffers

The patch restructures the tests in MultiviewDrawTests.cpp, so that
all rendering tests can be instantiated for side-by-side and layered
framebuffers.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I2c32fd3bd57b6afd1eb8d6cedb2d1b88b9fd6525
Reviewed-on: https://chromium-review.googlesource.com/627918
Commit-Queue: Martin Radev <ce534a10aebedcce16bec16367ddebba08bf8cf0@nvidia.com>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

MSOpenTech/angle,MSOpenTech/angle,ppy/angle,ppy/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,ppy/angle