scripts: Scan CWD in parameter validation script.
scripts: Scan CWD in parameter validation script.

This makes it more easy to locate the header in configs which have the
CWD set to something less obvious. In Chrome's case the build directory
is completely separated from the script directory.

Also reset the CWD after the header is found to keep the build intact.

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers