internal/system: relocate from system

These packages are highly specific to hakurei and are difficult to use safely from other pieces of code.

Their exported symbols are made available until v0.4.0 where they will be removed for #24.

Signed-off-by: Ophestra <cat@gensokyo.uk>

system/acl/deprecated.go

@@ -0,0 +1,25 @@
+// Package acl exposes the internal/system/acl package.
+//
+// Deprecated: This package will be removed in 0.4.
+package acl
+
+import (
+	_ "unsafe" // for go:linkname
+
+	"hakurei.app/internal/system/acl"
+)
+
+type Perm = acl.Perm
+
+const (
+	Read    = acl.Read
+	Write   = acl.Write
+	Execute = acl.Execute
+)
+
+// Update replaces ACL_USER entry with qualifier uid.
+//
+//go:linkname Update hakurei.app/internal/system/acl.Update
+func Update(name string, uid int, perms ...Perm) error
+
+type Perms = acl.Perms