To reduce the binary size of ANGLE, a gn override is added (glslang_angle) which: - Controls whether ENABLE_OPT=1 is set - Customizes the build for the Vulkan backend of ANGLE. As a first step, this removes HLSL functionality which together with no optimization shave ~2.5MB off of ANGLE's binary size. Upcoming changes will add a macro for GLSLANG_ANGLE similar to GLSLANG_WEB that will strip features from glslang to support only what ANGLE needs. Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>