refactor: Introduce all_streams_map.
refactor: Introduce all_streams_map.

We replace all_streams_id with a map.

We also use it to populate never_subscribed_streams.

And all_streams_map is a superset of stream_hash,
which we will soon kill off as well.

hackerkid/zulip,showell/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,showell/zulip,andersk/zulip,showell/zulip,zulip/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,kou/zulip,showell/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,showell/zulip,andersk/zulip,kou/zulip,zulip/zulip,punchagan/zulip,rht/zulip,rht/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip