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/Builtin.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <BAN/Function.h>
+#include <BAN/HashMap.h>
+#include <BAN/Iteration.h>
+#include <BAN/NoCopyMove.h>
+#include <BAN/String.h>
+
+#include <stdio.h>
+
+class Execute;
+
+class Builtin
+{
+	BAN_NON_COPYABLE(Builtin);
+	BAN_NON_MOVABLE(Builtin);
+public:
+	struct BuiltinCommand
+	{
+		using function_t = int (*)(Execute&, BAN::Span<const BAN::String>, FILE* fin, FILE* fout);
+
+		function_t function { nullptr };
+		bool immediate { false };
+
+		BuiltinCommand(function_t function, bool immediate)
+			: function(function)
+			, immediate(immediate)
+		{ }
+
+		BAN::ErrorOr<int> execute(Execute&, BAN::Span<const BAN::String> arguments, int fd_in, int fd_out) const;
+	};
+
+public:
+	Builtin() = default;
+	static Builtin& get()
+	{
+		static Builtin s_instance;
+		return s_instance;
+	}
+
+	void initialize();
+
+	void for_each_builtin(BAN::Function<BAN::Iteration(BAN::StringView, const BuiltinCommand&)>) const;
+
+	// return nullptr if not found
+	const BuiltinCommand* find_builtin(const BAN::String& name) const;
+
+private:
+	BAN::HashMap<BAN::String, BuiltinCommand> m_builtin_commands;
+};