Fix #7386: Measurement tooltip for tunnels, aqueducts & docks did not display or flickered.

Measurement tooltip was auto-closed as the hover/right-click test for tooltips was not
satisfied in this case. This is fixed by keeping the tooltip visible and instead explicitly
closing the tooltip when the PlaceObject is cancelled/completed.

src/window_gui.h

@@ -873,8 +873,8 @@ void RelocateAllWindows(int neww, int newh);
 /* misc_gui.cpp */
 enum TooltipCloseCondition {
 	TCC_RIGHT_CLICK,
-	TCC_LEFT_CLICK,
 	TCC_HOVER,
+	TCC_NONE,
 };
 
 void GuiShowTooltips(Window *parent, StringID str, uint paramcount = 0, const uint64 params[] = NULL, TooltipCloseCondition close_tooltip = TCC_HOVER);