Shell: rewrite the whole shell to use tokens instead of raw strings

tab completion is still running with raw strings and that has to be
fixed in the future.

userspace/programs/Shell/Alias.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <BAN/Function.h>
+#include <BAN/HashMap.h>
+#include <BAN/Iteration.h>
+#include <BAN/NoCopyMove.h>
+#include <BAN/String.h>
+
+class Alias
+{
+	BAN_NON_COPYABLE(Alias);
+	BAN_NON_MOVABLE(Alias);
+public:
+	Alias() = default;
+	static Alias& get()
+	{
+		static Alias s_instance;
+		return s_instance;
+	}
+
+	BAN::ErrorOr<void> set_alias(BAN::StringView name, BAN::StringView value);
+
+	// NOTE: `const BAN::String&` instead of `BAN::StringView` to avoid BAN::String construction
+	//       for hashmap accesses
+	BAN::Optional<BAN::StringView> get_alias(const BAN::String& name) const;
+
+	void for_each_alias(BAN::Function<BAN::Iteration(BAN::StringView, BAN::StringView)>) const;
+
+private:
+	BAN::HashMap<BAN::String, BAN::String> m_aliases;
+};