Add missing NV_EXTENSIONS ifdef

Support GL_ARB_fragment_shader_interlock

Remove glslang.y from gn sources

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.

with subgroup touch tests (error and non-error cases)
Currently the subgroup built-ins are NOT giving the correct output.
This is fixed in the next commit.

with subgroup touch testing (error and non-error cases)

Add missing symbolTable.relateToOperator("subgroupMemoryBarrierShared") call for
Mesh/Task shaders so they don't assert in ParseHelper.cpp

Touch test all subgroup builtins in vert, tesc, tese, geom, frag, compute shaders
before and after enabling extensions to make sure the correct errors are generated
and then not generated (after enablement).

Allow runtime-sized arrays of acceleration structures

Misc fixes from dgkoch

Don't prefix with "Capability" since the majority of them don't.
Also add missing CapabilityImageFootprintNV

Fixed .dll install on MSVC.

No behavior changes.  Please see [1] for why this is necessary.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=964411

Build.gn: allow optimization in glslang lib and standalone

Update SPIRV-Tools, SPIRV-Headers

Headers update fixes validation of spv.shaderBallotAMD.

SPV 1.4: Add code generation for SPIR-V 1.4 features

...when doing a variable lookup on an array of constants.

This includes the test for the first feature of OpEntryPoint.

Latest known-good SPIRV-Tools: WARNING: Needs python 3.x.

You may need to install python 3.x and also
[windows users] may need to get it in your path in front of python 2.7.x.

If you don't need the external projects (i.e., SPIRV-Tools) and don't want
to upgrade to python 3, don't create the External subdirectory and CMake
won't require python 3.  (CMake has a bug that makes it find the wrong one
on a first pass if the top level does not require the version needed by
lower levels.)

For nonuniformEXT constructor, make a copy of the node to decorate

Add support for GL_EXT_buffer_reference2