GL_EXT_mesh_shader/SPV_EXT_mesh_shader implementation

Added following updates to GL_EXT_mesh_shader implementation:

1. Added SPIRV and GLSL test cases
2. Added checks to ensure NV and EXT mesh shader builtins cannot be used interchangeably.
3. Updated the language name by removing the postfix "NV" to MeshShader and TaskShader.
4. Added checks for grammar checking to comply with the spec.

5. Added gl_NumWorkGroups builtin to Mesh shader
6. Fixed data type of gl_PrimitiveLineIndicesEXT and gl_PrimitiveTriangleIndicesEXT
7. Added new constants to the resources table
8. Updates to handle new storage qualifier "taskPayloadSharedEXT"
9. Updated test cases by replacing "taskEXT" with storage qualifier "taskPayloadSharedEXT"

Addressed  Review comments
1. Fixed instruction description used by glslang disassembly.
2. Updated OpEmitMeshTasksEXT as per spec update
3. Fixed implementation that errors out if there are more then one taskPayloadSharedEXT varjables.
4. Fixed miscellaneous error logs and removed unwanted code.

SPIRV 1.6 related build failure fixes
- Update SPIRV header to 1.6
- Fix conflict wiht SPIRV 1.6 change, where localSizeId is used for execution mode for mesh/task shaders

Enable SPIRV generated for EXT_mesh_shader to be version 1.4

GL_EXT_mesh_shader: Add checks for atomic support and corresponding test cases

glslang/Include/Types.h

@@ -833,7 +833,7 @@ public:
             }
             storage = EvqUniform;
             break;
-        case EbsStorageBuffer : 
+        case EbsStorageBuffer :
             storage = EvqBuffer;
             break;
 #ifndef GLSLANG_WEB
@@ -856,6 +856,7 @@ public:
     bool isPerPrimitive() const { return perPrimitiveNV; }
     bool isPerView() const { return perViewNV; }
     bool isTaskMemory() const { return perTaskNV; }
+    bool isTaskPayload() const { return storage == EvqtaskPayloadSharedEXT; }
     bool isAnyPayload() const {
         return storage == EvqPayload || storage == EvqPayloadIn;
     }
@@ -874,8 +875,8 @@ public:
         case EShLangTessEvaluation:
             return ! patch && isPipeInput();
         case EShLangFragment:
-            return (pervertexNV || pervertexEXT) && isPipeInput();
-        case EShLangMeshNV:
+            return pervertexNV && isPipeInput();
+        case EShLangMesh:
             return ! perTaskNV && isPipeOutput();
 
         default:
@@ -2543,7 +2544,7 @@ public:
     void setStruct(TTypeList* s) { assert(isStruct()); structure = s; }
     TTypeList* getWritableStruct() const { assert(isStruct()); return structure; }  // This should only be used when known to not be sharing with other threads
     void setBasicType(const TBasicType& t) { basicType = t; }
-    
+
     int computeNumComponents() const
     {
         int components = 0;