Vulkan: Require Android NDK API level 26, dropping Android N support. Due to Vulkan Validation Layers breaking Android N backward compatibility. See http://crrev/c/1405714 and https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues/623 Bug: angleproject:3095 Change-Id: I5da306c567cd9a0088149ca9929b38c8ed2cc86a Reviewed-on: https://chromium-review.googlesource.com/c/1465954 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org>