[kernel] Have process_start syscall take a list of handles

This also prompted a change of the process initialization protocol to
allow handles to get typed, and changing to marking them as just
self/other handls. This also means exposing the object type enum to
userspace.

src/kernel/syscalls/process.cpp

@@ -16,8 +16,18 @@ process_create(j6_handle_t *handle)
 }
 
 j6_status_t
-process_start(j6_handle_t *handle, uintptr_t entrypoint)
+process_start(j6_handle_t handle, uintptr_t entrypoint, j6_handle_t *handles, size_t handle_count)
 {
+	process &p = process::current();
+	process *c = get_handle<process>(handle);
+	if (handle_count && !handles)
+		return j6_err_invalid_arg;
+
+	for (size_t i = 0; i < handle_count; ++i) {
+		kobject *o = p.lookup_handle(handles[i]);
+		if (o) c->add_handle(o);
+	}
+
 	return j6_err_nyi;
 }