Vulkan: Allow user to specify preferred device On a platform with multiple graphics devices (e.g. laptop with integrated and descrete devices) it's handy to be able to specify the specific device we want ANGLE to use. Setting the environment variable ANGLE_PREFERRED_DEVICE to the device name as returned by VkPhysicalDeviceProperties.deviceName will select that device. Bug: angleproject:4305 Change-Id: Ib16895add2c36a59135942b52401ceb7b6bc0895 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2002737 Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>