Further VK_NV_mesh_shader test variants and fixes

Further VK_NV_mesh_shader test variants and fixes

* Add local_size/vertices/primitives maximization cases.

* Add task, mesh and fragment interface variable tests.

* Increase glslang NV mesh shader built-in limits (they need to be as
  big as exposed by other interesting implementations like RADV and used
  in some tests).

* Replace tcu::nothing<T> with tcu::Nothing in misc tests.

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

Components: Vulkan
VK-GL-CTS issue: 2991

Change-Id: I5eead8177b6315a44bb95c820af4549028ba5572