Allow navigating with forward&back mouse buttons from CMake and ManPage home pages

Before this change the forward/back mouse button navigation worked in
QtHelp home pages and all non-home pages.
1 job for !112 with documentation-view-forward-back-mouse-buttons in 44 minutes and 28 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
passed #35264
linux kf5-qt5 qt5.12

00:44:28

41.0%