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.subgroupQuad.comp.out

@@ -12,8 +12,8 @@ local_size = (8, 1, 1)
 0:16          'invocation' ( temp highp uint)
 0:16          mod ( temp mediump uint)
 0:16            add ( temp mediump uint)
-0:16              'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
-0:16              'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
+0:16              'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
+0:16              'gl_SubgroupSize' ( in mediump uint SubgroupSize)
 0:16            Constant:
 0:16              4 (const uint)
 0:18      move second child to first child ( temp highp float)
@@ -1728,8 +1728,8 @@ local_size = (8, 1, 1)
 0:16          'invocation' ( temp highp uint)
 0:16          mod ( temp mediump uint)
 0:16            add ( temp mediump uint)
-0:16              'gl_SubgroupInvocationID' ( in mediump uint unknown built-in variable)
-0:16              'gl_SubgroupSize' ( in mediump uint unknown built-in variable)
+0:16              'gl_SubgroupInvocationID' ( in mediump uint SubgroupInvocationID)
+0:16              'gl_SubgroupSize' ( in mediump uint SubgroupSize)
 0:16            Constant:
 0:16              4 (const uint)
 0:18      move second child to first child ( temp highp float)