chore: Split the main fastly interface of fastly.wit (#609)

Author: elliottt

ci/clang-format.ignore

@@ -1,3 +1,4 @@
 runtime/js-compute-runtime/third_party/wizer.h
 runtime/js-compute-runtime/rust-url/rust-url.h
 runtime/js-compute-runtime/rust-encoding/rust-encoding.h
+runtime/js-compute-runtime/fastly-world/fastly_world.h