Actually sdk-1.2.154.1 for Vulkan-Loader.
glslang is updated to bacaef3237c515e40d1a24722be48c0a0b30f75f which is the
known-good version for Vulkan-ValidationLayers 1.2.154.0.
COPYRIGHT.txt was synced with the current version of the glslang LICENSE.txt,
and `glslang/register_types.cpp` now uses the upstream definition for its
default builtin resource instead of hardcoding it.
- Renamed option to `builtin_vulkan`, since that's the name of the
library and if we were to add new components, we'd likely use that
same option.
- Merge `vulkan_loader/SCsub` in `vulkan/SCsub`.
- Accordingly, don't use built-in Vulkan headers when not building
against the built-in loader library.
- Drop Vulkan registry which we don't appear to need currently.
- Style and permission fixes.
