display: Ensure configuration has the expected type

In almost all cases, the configuration will be "valid" in the sense that
g-c-c can represent it in the UI. However, there are cases like
mirroring setups with three monitors that we do not allow.

In case that the user has such a configuration, ensure that the
configuration we represent is actually valid according to our
expectations. This should not affect normal use cases, but allows users
to recover again if the configuration is broken for some reason.

Fixes #383
11 jobs for benzea/ensure-valid-config-after-loading in 4 minutes and 13 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #250122
build

00:02:17

 
  Test
passed #250124
asan

00:01:55

passed #250123
test

00:00:58

 
  Manual
manual #250129
allowed to fail manual
armv8
manual #250125
allowed to fail manual
flatpak
manual #250128
allowed to fail manual
msan
manual #250130
allowed to fail manual
ppc64le
manual #250126
allowed to fail manual
tsan
manual #250127
allowed to fail manual
ubsan
 
  Review
manual #250131
allowed to fail manual
review
manual #250132
allowed to fail manual
stop_review