preferences-window: Make it a HdyDialog

This makes the preferences window fully adaptive.
7 jobs for preferences-window-adaptive-dialog in 9 minutes and 57 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #82516
librem5
build-debian-clang

00:02:32

passed #82514
librem5
build-debian-gcc

00:02:04

passed #82515
librem5
build-debian-gcc-static

00:02:01

passed #82517
librem5
build-fedora-gcc

00:02:41

 
  Docs
passed #82518
librem5
build-gtkdoc

00:01:40

 
  Test
passed #82519
librem5
unit-test

00:01:29

46.3%
 
  Package
passed #82520
librem5
package-debian

00:01:44