In 2.18, when in “unread” mode, if there were no unread items,
clicking the button would clear out all items and trigger a reload
or refresh status of the “Load more” button, depending on whether
the client was aware of more unread items on the server.

When we ported entries to React in f3b279c,
we accidentally broke the “Mark all as read” button,
making it keep all the items it marked in the view (a).
We also did not port the code that would load more items afterwards (b).

It got further broken during porting routing to React in 405a3ec.
We looked for the `filter` field on a wrong object (c).

We fixed (c) and attempted to fix (a) in ec544b7
but the patch just made it keep all the items it did not mark, such as those marked as read
manually beforehand, instead.

This patch makes it so that the button removes all the items in the view except for the active item
and loads more items afterwards, returning to behaviour similar to 2.18.

Since we currently do not have a sane dispatch method in EntriesPage,
we unfortunately have to trigger a virtual click on the “Load more” button.
To make that work, we also need to keep the old offsets since when we clear the entries,
there would be no way to get the offsets back in the `moreOnClick` handler.

This does not help since the offset is only calculated on pressing the button (initially undefined).

This is still somewhat broken: switching filter will trigger `RESET_OFFSET`,
which will start loading more, and its spinner will get stuck.

The aborting short circuit has been introduced in 28d27f3

It can happen that the request is cancelled by another request but the second request
will use `setLoadingState` instead of `setMoreLoadingState` so `moreLoadingState` will be stuck on `LOADING`.

Not sure if it this cannot introduce a race if the same state is used in both requests.

Tried testing with {let a = new AbortController(); let f = fetch('wait.php?seconds=3', {signal: a.signal}); f.then(r => console.log(r, a)); setTimeout(() => {a.abort(); f.then((r) => console.log(r, a.signal))}, 100);}