Use spirv.h from the Vulkan SDK

If the project's dependency is the Vulkan SDK, why is the spirv.h copy needed?

If it's there to allow people to use spirv-reflect without the Vulkan SDK, it would still be nice to have the option to use the SDK's version through a define.

Start by locating the bundled spirv.h copy and the project's Vulkan SDK dependency or build configuration. Check how SPIRV-Reflect currently includes this header and identify the existing define or configuration entry points, if any. Done means builds can use the SDK's version while retaining a usable path without the SDK, with both configurations validated.

Written by the indexing model from the issue text.