Fix subgroup support for ray tracing

Closes #1735

GlslangToSpv.cpp
- minor formatting cleanup

BaseTypes.h
- minor formatting cleanup
- add subgroup builtins to GetBuiltInVariableString
  (was resulting in "unknown built-in variable" messages in test output)

Initialize.cpp
- better naming and re-use of strings for subgroup builtin variable declarations
- define subgroup builtin variables in ray-tracing shaders

intermOut.cpp
- add handling of the EOpSubgroupParition* variables
  (was resulting in "ERROR: Bad aggregation op" messages in test output)

Update test results.

Test/baseResults/glsl.es320.subgroupClusteredNeg.comp.out

@@ -26,8 +26,8 @@ ERROR: node is still EOpNull!
 0:19          'invocation' ( temp highp uint)
 0:19          mod ( temp mediump uint)
 0:19            add ( temp mediump uint)
-0:19              'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
-0:19              'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
+0:19              'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
+0:19              'gl_SubgroupSize' ( in mediump uint SubgroupSize)
 0:19            Constant:
 0:19              4 (const uint)
 0:21      move second child to first child ( temp highp 2-component vector of float)
@@ -325,8 +325,8 @@ ERROR: node is still EOpNull!
 0:19          'invocation' ( temp highp uint)
 0:19          mod ( temp mediump uint)
 0:19            add ( temp mediump uint)
-0:19              'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
-0:19              'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
+0:19              'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
+0:19              'gl_SubgroupSize' ( in mediump uint SubgroupSize)
 0:19            Constant:
 0:19              4 (const uint)
 0:21      move second child to first child ( temp highp 2-component vector of float)