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 14 seconds
Status Job ID Name Coverage
  Build
passed #367576
librem5
build-pureos-gcc-byzantium

00:01:45

 
  Test
passed #367578
librem5
check-po

00:00:14

passed #367577
librem5
test:debian-gcc

00:03:25

22.3%
 
  Package
passed #367579
librem5
package-pureos-byzantium

00:01:48

passed #367580
librem5:arm64
package-pureos-byzantium:arm64

00:05:03

 
  Test Package
passed #367581
librem5
autopkgtest-pureos-byzantium-package

00:01:16

passed #367582
librem5
lintian-pureos-byzantium-package

00:00:44