kernel: Rewrite bufNormalize

This is a complete rewrite of the RTLIL-kernel-side bufnorm code. This
is done to support inout ports and undirected connections as well as to
allow removal of cells while in bufnorm mode.

This doesn't yet update the (experimental) `bufnorm` pass, so to
manually test the new kernel functionality, it is important to only use
`bufnorm -update` and `bufnorm -reset` which rely entirely on the kernel
functionality. Other modes of the `bufnorm` pass may still fail in the
presence of inout ports or undirected connections.

kernel/rtlil.h

@@ -1337,6 +1337,7 @@ public:
 	bool is_fully_def() const;
 	bool is_fully_undef() const;
 	bool has_const() const;
+	bool has_const(State state) const;
 	bool has_marked_bits() const;
 	bool is_onehot(int *pos = nullptr) const;
 
@@ -1728,7 +1729,11 @@ public:
 	std::vector<RTLIL::IdString> ports;
 	void fixup_ports();
 
-	pool<pair<RTLIL::Cell*, RTLIL::IdString>> bufNormQueue;
+	pool<RTLIL::Cell *> buf_norm_cell_queue;
+	pool<pair<RTLIL::Cell *, RTLIL::IdString>> buf_norm_cell_port_queue;
+	pool<RTLIL::Wire *> buf_norm_wire_queue;
+	pool<RTLIL::Cell *> pending_deleted_cells;
+	dict<RTLIL::Wire *, pool<RTLIL::Cell *>> buf_norm_connect_index;
 	void bufNormalize();
 
 	template<typename T> void rewrite_sigspecs(T &functor);