preferences-window: Hide filtered-out rows

The CSS engine works in such a way that invisible children are treated
as visible widgets, which breaks the expectations of the .preferences
style class when filtering a row, leading to straight corners when the
first row or last row are filtered out.

This works around it by hiding filtered out widgets.
11 jobs for toggle-search-result-visibility in 37 minutes and 5 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #256049
librem5
api-visibility

00:02:52

passed #256051
librem5
build-debian-clang

00:04:47

passed #256050
librem5
build-debian-gcc

00:03:32

passed #256052
librem5
build-fedora-gcc

00:15:55

 
  Test+Docs
passed #256053
librem5
build-gtkdoc

00:03:10

passed #256054
librem5
unit-test

00:03:06

43.7%
 
  Package
passed #256055
librem5
package-debian-buster

00:03:46

passed #256056
librem5:arm64
package-debian-buster:arm64

00:06:27

failed #256057
flatpak allowed to fail
package-flatpak

00:00:09

 
  Test Package
passed #256058
librem5
autopkgtest-debian-buster-package

00:03:29

passed #256059
librem5
lintian-debian-buster-package

00:01:18

 
Name Stage Failure
failed
package-flatpak Package There has been a runner system failure, please try again
Running with gitlab-runner 12.6.0 (ac8e767a)
on arm01-runner 53gNDtDb
ERROR: Preparation failed: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? (executor_docker.go:982:0s)
Will be retried in 3s ...
ERROR: Preparation failed: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? (executor_docker.go:982:0s)
Will be retried in 3s ...
ERROR: Preparation failed: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? (executor_docker.go:982:0s)
Will be retried in 3s ...
ERROR: Job failed (system failure): Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? (executor_docker.go:982:0s)