chat-view: Add support for selecting multiple files

This is currently unused, but shall be used when MMS support
has landed
7 jobs for wip/sadiq/attachment in 12 minutes and 30 seconds (queued for 2 minutes and 18 seconds)
Status Name Job ID Coverage
  Build
passed build-pureos-gcc-byzantium #368996
librem5

00:03:32

 
  Test
passed check-po #368998
librem5

00:00:25

passed test:debian-gcc #368997
librem5

00:02:58

21.6%
 
  Package
passed package-pureos-byzantium #368999
librem5

00:01:50

passed package-pureos-byzantium:arm64 #369000
librem5:arm64

00:05:34

 
  Test Package
passed autopkgtest-pureos-byzantium-package #369001
librem5

00:01:19

passed lintian-pureos-byzantium-package #369002
librem5

00:00:51