Add Vulkan compute level system feature

The names of specific Vulkan API features can't be documented yet,
because they won't be ratified by Khronos before the documentation
becomes public in a developer preview.

Bug: 34745152
Test: android.graphics.cts.VulkanFeaturesTest
Change-Id: I9af673bcb5b0c74bde72ab7a579573894170a55d