When starting the view builder, we find all existing views in
`calculate_shard_build_step` and then register a listener for new views.
Between these steps we may yield and create a new view, then we miss
initializing the view build step for the new view, and we won't start
building it.
To fix this we first register the listener and then read existing views,
so a view can't be missed.
Fixesscylladb/scylladb#20338Closesscylladb/scylladb#22184
2a8ff478f0