SPV: Implement new extensions GL_KHX_device_group and GL_KHX_multiview.

These correspond to SPV_KHR_device_group and SPV_KHR_multiview.
Also, bring tests up to date with Khronos internals, and some misc. related changes.

glslang/Include/BaseTypes.h

@@ -203,6 +203,9 @@ enum TBuiltInVariable {
     EbvBaryCoordPullModel,
 #endif
 
+    EbvViewIndex,
+    EbvDeviceIndex,
+
 #ifdef NV_EXTENSIONS
     EbvViewportMaskNV,
     EbvSecondaryPositionNV,
@@ -210,6 +213,7 @@ enum TBuiltInVariable {
     EbvPositionPerViewNV,
     EbvViewportMaskPerViewNV,
 #endif 
+
     // HLSL built-ins that live only temporarily, until they get remapped
     // to one of the above.
     EbvFragDepthGreater,