Use the lightweight tour launcher

Use the `mw.guidedTour.launcher.launchTour` method to defer loading the
ext.guidedTour.lib library until a tour needs to be launched.

Bug: 65734
Change-Id: I935582d2d07cc0a8e3e2db1c205aa920abda0579
Depends-On: Ib187a252acfb17749e1852e491a83d4aa5619cd8