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.
diff --git a/Test/baseResults/glsl.es320.subgroup.tese.out b/Test/baseResults/glsl.es320.subgroup.tese.out
index acde7db..29f7b73 100644
--- a/Test/baseResults/glsl.es320.subgroup.tese.out
+++ b/Test/baseResults/glsl.es320.subgroup.tese.out
@@ -16,8 +16,8 @@
 0:11              0 (const uint)
 0:11          'gl_PrimitiveID' ( in highp int PrimitiveID)
 0:11        Construct uvec4 ( temp highp 4-component vector of uint)
-0:11          'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
-0:11          'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
+0:11          'gl_SubgroupSize' ( in mediump uint SubgroupSize)
+0:11          'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
 0:11          Constant:
 0:11            0 (const uint)
 0:11          Constant:
@@ -46,8 +46,8 @@
 0:11              0 (const uint)
 0:11          'gl_PrimitiveID' ( in highp int PrimitiveID)
 0:11        Construct uvec4 ( temp highp 4-component vector of uint)
-0:11          'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
-0:11          'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
+0:11          'gl_SubgroupSize' ( in mediump uint SubgroupSize)
+0:11          'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
 0:11          Constant:
 0:11            0 (const uint)
 0:11          Constant: