Add tests for VK_NV_mesh_shader

Add tests for VK_NV_mesh_shader

Tests that verify multiple aspects of mesh shader pipelines work as
expected. This includes:

* Some basic smoke tests.
* API tests to check the new draw calls and different rules about them.
* Synchronization tests.
* Test a wide range of affected built-in variables.
* Miscellaneous tests:
  * Producing small and large amounts of different types of primitives.
  * Barriers.
  * Push constants.
  * Custom per-primitive attributes.
  * Complex structures in the task->mesh interface.

New tests:
dEQP-VK.mesh_shader.nv.*

Components: Vulkan, Framework
VK-GL-CTS issue: 2991

Change-Id: I510296e4da326a2f0a3891d55a1116848d874c3f