Add SBAT support, when -Dsbat-distro value is specified. One can use -Dsbat-distro=auto for autodetection of all sbat options. Many meson configure options added to customize SBAT CSV values, but sensible defaults are auto detected by default. SBAT support is required if shim v15+ is used to load systemd-boot binary or kernel.efi (Type II BootLoaderSpec). Fixes #19247