Rename programmable signals to programmable pre-signals

This is to make it less unclear what they actually are and do

src/rail_cmd.cpp

@@ -1550,7 +1550,7 @@ CommandCost CmdBuildSingleSignal(TileIndex tile, DoCommandFlag flags, uint32 p1,
 						SetPresentSignals(tile, (GetPresentSignals(tile) & ~SignalOnTrack(track)) | KillFirstBit(SignalOnTrack(track)));
 					}
 				} else {
-					/* programmable signal dependencies are invalidated when the signal direction is changed */
+					/* programmable pre-signal dependencies are invalidated when the signal direction is changed */
 					CheckRemoveSignal(tile, track);
 					/* cycle the signal side: both -> left -> right -> both -> ... */
 					CycleSignalSide(tile, track);