BUILD.gn: glslang_sources need the public config too

BUILD.gn: only use complete_static_lib on mac

Add ES 320 support and additional error checks for SPV_NV_mesh_shader

Also continue error checking post requireStage() check

BUILD.gn: make the static_lib complete to fix the build on OSX

This also fixes some cpp files that uncover issues when building
with the flags turned off.

Remove NV_EXTENSION ifdefs from ShaderLang.h

This allows library consumers to work without have to set
NV_EXTENSIONS.

Fix missing case label for miss stage.

Add BUILD.gn configuration.

- Add ES 320 support
- Error out use of perprimitiveNV for non mesh/fragment shaders
- Error out use of mesh/task shaders w/o use of NV_mesh_shader
- Error out use of NV_mesh_shader for non task/mesh shaders
- Error out use of perviewNV for non mesh shaders
- Error out use of taskNV for non mesh/task shaders
- Add test case for mesh shader with ES 320 profile

This CL adds the necessary configuration to build glslang inside a
Chromium checkout. Two build warnings were fixed in the process to
make things compile.

Update known-good to tools/headers for the Nvidia Turing extensions.

Add support for multiple Nvidia extensions

Add GL_EXT_shader_atomic_int64