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>