mesonlib: use Literal to tighten configure_file formats
mesonlib: use Literal to tighten configure_file formats

Now that we have strong type checking in the interpreter, we can tighten
the type checking in the mesonlib side by using the same Literals.

mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson