menu: Use GtkPopoverMenu instead of GtkMenu for primary menu

Popovers are recommended for primary menus; In addition, the
migration from the app menu introduced new conventions like
using "About [App]" instead of "About", and grouping
Preferences with About, Help, and Keyboard Shortcuts.
2 jobs from use-popover-instead-of-menu in 14 minutes and 26 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #162548
build

00:13:53

 
  Test Results
passed #162549
test-results

00:00:32