Or else frozensets are excluded. This will be useful in an upcoming
commit where I plan to change a function that accepts `List[str]` to
accept `StrCollection` instead.

I am about to make use of this exclusion mechanism to exclude rooms for
a specific user and a specific sync. This rename helps to clarify the
distinction between the global config and the rooms to exclude for a
specific sync.

I plan to feed a list of partially stated rooms for this sync to ignore

using the mechanism established in the previous commit

So that we can work out which rooms have become fully-stated during a
given sync period.

This was fouling up a complement test added alongside this PR.
Excluding a room would mean the set of forgotten rooms in the cache
would be extended. This means that room could be erroneously considered
forgotten in the future.

Introduced in #12310, Synapse 1.57.0. I don't think this had any
user-visible side effects (until now).

Similar plan as before. We've omitted rooms from certain sync responses;
now we establish the mechanism to reintroduce them into future syncs.

for eager incremental syncs only, provided they're still fully stated

…ster-joins

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

…ster-joins

Thanks MV :)

Co-authored-by: Mathieu Velen <mathieuv@matrix.org>