region: Add description label and use icon for options button

As per design:
https://wiki.gnome.org/Design/SystemSettings/RegionAndLanguage
11 jobs for region-input-design in 3 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #107236
build

00:02:08

 
  Test
passed #107238
asan

00:01:40

passed #107237
test

00:00:39

 
  Manual
manual #107243
allowed to fail manual
armv8
manual #107239
allowed to fail manual
flatpak
manual #107242
allowed to fail manual
msan
manual #107244
allowed to fail manual
ppc64le
manual #107240
allowed to fail manual
tsan
manual #107241
allowed to fail manual
ubsan
 
  Review
manual #107245
allowed to fail manual
review
manual #107246
allowed to fail manual
stop_review