examples: Add the View Switcher page

This example presents a HdyViewSwitcher and a HdyViewSwitcherBar in
their own window. Currently both are visible at the same time, a later
commit should make only one visible at a time, depending on the
available width.
5 jobs for view-switcher in 4 minutes and 28 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #20709
librem5
build-debian-clang

00:03:10

passed #20707
librem5
build-debian-gcc

00:03:37

39.0%
passed #20708
librem5
build-debian-gcc-static

00:02:22

passed #20711
librem5
build-debian-package

00:02:04

passed #20710
librem5
build-fedora-gcc

00:03:00