Allow GL_NV_mesh_shader in fragment shaders for perprimitiveNV

- Emit relevant capability/extension for use of perprimitiveNV in fragment shader
- Remove redundant checks for mesh shader qualifiers in glslang.y
- Add profile version check for use of extension GL_NV_mesh_shader
- Add a new gtest for use of perprimitiveNV in fragment shader

glslang/MachineIndependent/ParseHelper.cpp

@@ -4514,6 +4514,8 @@ void TParseContext::finish()
         break;
 #ifdef NV_EXTENSIONS
     case EShLangTaskNV:
+        requireExtensions(getCurrentLoc(), 1, &E_GL_NV_mesh_shader, "task shaders");
+        break;
     case EShLangMeshNV:
         requireExtensions(getCurrentLoc(), 1, &E_GL_NV_mesh_shader, "mesh shaders");
         break;