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 10 minutes and 4 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #366722
librem5
build-pureos-gcc-byzantium

00:01:45

 
  Test
passed #366724
librem5
check-po

00:00:14

passed #366723
librem5
test:debian-gcc

00:03:24

22.9%
 
  Package
passed #366725
librem5
package-pureos-byzantium

00:01:36

passed #366726
librem5:arm64
package-pureos-byzantium:arm64

00:04:51

 
  Test Package
passed #366727
librem5
autopkgtest-pureos-byzantium-package

00:01:17

passed #366728
librem5
lintian-pureos-byzantium-package

00:00:36