region: Change format chooser dialog to match design

Adjust spacing and move the search field to the top as per:
https://wiki.gnome.org/Design/SystemSettings/RegionAndLanguage
11 jobs for region-format-dialog in 3 minutes and 12 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #146263
build

00:02:01

 
  Test
passed #146265
asan

00:01:09

passed #146264
test

00:00:42

 
  Manual
manual #146270
allowed to fail manual
armv8
manual #146266
allowed to fail manual
flatpak
manual #146269
allowed to fail manual
msan
manual #146271
allowed to fail manual
ppc64le
manual #146267
allowed to fail manual
tsan
manual #146268
allowed to fail manual
ubsan
 
  Review
manual #146272
allowed to fail manual
review
manual #146273
allowed to fail manual
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