feat(init): add init crate with declarative boot manifest, boot sequence, supervisor and shutdown stubs

Also: make types from_raw/raw const fn, add create_process/kill/delegate/revoke to userspace syscall stubs.

crates/init/src/shutdown.rs

@@ -0,0 +1,3 @@
+pub fn shutdown() -> ! {
+    userspace::syscall::exit();
+}