Add voters count support

[ClearlyClaire]

For newly-created polls, count voters in addition to the number of votes.
Present them in the REST API as voters_count and over ActivityPub as toot:votersCount.

When that information is available, the text now says “X voters” instead of “X votes”, and the tallies use that for percentages instead of the total number of votes (which is far less useful for anyOf polls)

Marked as a draft because it probably could use more tests, and I'm very unsure about the attribute it should use.

[Gargron]

I'm hesitant to add another custom property. Is the problem being solved the confusion around submitting another multiple-choice vote -> number of votes going up? That doesn't seem wrong to me per se.

[ClearlyClaire]

It's not just that. 40 people voting just one option each is indistinguishable from 10 people all voting all the options, although those have very different meanings ultimately

[trwnh]

instead of votersCount i would propose something like using totalItems of the replies Collection. whether the Question is oneOf or anyOf should be irrelevant; each reply should contain an array of the selected answers.

[ClearlyClaire]

@trwnh no, that would mean listing all the votes, and each vote is for one option only, so that would just be equivalent to what we currently do

[trwnh]

Wait, so one vote creates multiple responses? That doesn't make sense...

[ClearlyClaire]

Yes, a vote is a reply object with the same name as the option it is for, voting multiple options require multiple such objects.

[ClearlyClaire]

Marked as ready for review as there seem to be an agreement that the AS vocabulary isn't enough for this and pleroma devs are ok with the chosen attribute name.